<header>
			<h1 class="blog-post__title">Power and Efficiency</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="power">Power</h2>

Power is the rate of using energy.

Power is measured in Watts (W). 1W is 1J of energy being used per second.

<img src="/img/notes/12/Capture.jpg" alt="Power and Efficiency, figure 1" /></a>

A 100W light bulb will use more electrical energy than a 60W bulb if they are both on for the same length of time.

You need to remember the equation for power for your exam:

<h2 class="ql-align-center">P = E ÷ t</h2>

__P __= power (W)

E = work done or energy transferred (J)

t = time (s)

<img src="/img/notes/01/a.png" alt="Power and Efficiency, figure 2" /></a>

There are also two other equations for power that you need to memorise which will be covered in more detail in the electricity lessons.

Power = Current x Voltage

<h2 class="ql-align-center">P = IV</h2>

<img src="/img/notes/01/b.png" alt="Power and Efficiency, figure 3" /></a>

And:

Power = Current2__ x Resistance__

<h2 class="ql-align-center">P = I2R</h2>

<h2 id="converting-units">Converting Units</h2>

It is important to be able to convert units as power is often given in kilowatts (kW).

1 kW = 1000W

To change W into kW, divide by 1000.

To change kW into W, multiply by 1000.

Worked Example

<img src="/img/notes/01/d.png" alt="Power and Efficiency, figure 1" /></a>

A weightlifter raises a bar from the floor to above his head. To lift the bar, the weightlifter does 5kJ of work in 2.5s.

Calculate the power he produced:

<ol>
 <li>Power = energy ÷ time</li>
 <li>5kJ = 5000J</li>
 <li>Power = 5000 ÷ 2.5 = 2000 W</li>
</ol>

Another weightlifter lifts the same weight in a shorter time. Compare the power of the two weightlifters.

<ol>
 <li>Using the same amount of energy in a shorter time would require more power</li>
</ol>

<h2 id="sankey-diagrams">Sankey Diagrams</h2>

Sankey diagrams were introduced in a previous lesson. They can be used to calculate efficiency.

<img src="/img/notes/12/3.jpg" alt="Power and Efficiency, figure 1" /></a>

For this Sankey diagram, the useful energy output is 10J and the total energy input is 60J. Therefore, the efficiency is 10÷60=0.17 (or 17%)

<h2 id="efficiency">Efficiency</h2>

All devices waste some energy, usually as heat due to friction between moving parts.

<ol>
 <li>For example, a light bulb is designed to produce light, but also produces heat energy which is dissipated into the surroundings.</li>
 <li>A car engine is designed to produce kinetic energy but also produces heat and sound which is dissipated into the surroundings.</li>
</ol>

Efficiency is a measurement of how much energy is converted usefully (compared to how much is wasted).

You need to remember the equations for efficiency:

<h2 class="ql-align-center">Efficiency = useful energy out ÷ total energy in</h2>

Or

<h2 class="ql-align-center">Efficiency = useful power out ÷ total power in</h2>

Efficiency has no units!

It can be written as a number between 0 and 1 or as a %. For example, an efficiency of 0.25 is the same as an efficiency of 25%.

Because some energy is always wasted from every device, efficiency should always be less than 1 or less than 100%. If you get answer that is bigger than 1 or 100%, you have made a mistake somewhere in your calculation!

Worked Examples

<img src="/img/notes/01/drill-1295561_960_720-290x300.png" alt="Power and Efficiency, figure 1" /></a>

A power drill uses 500J of electricity. Only 400J of kinetic energy was generated by the drill. What is its efficiency?

<ol>
 <li>Efficiency = useful energy out ÷ total energy in</li>
 <li>Efficiency = 400 ÷ 500</li>
 <li>Efficiency = 0.8 (or 80%)</li>
</ol>

<img src="/img/notes/12/Capture2.jpg" alt="Power and Efficiency, figure 2" /></a>

A portable speaker coverts 150J of electrical energy into 30J of sound energy. Calculate its efficiency.

<ol>
 <li>Efficiency = useful energy out ÷ total energy in</li>
 <li>Efficiency = 30 ÷ 150</li>
 <li>Efficiency = 0.2 (or 20%)</li>
</ol>

<h2 id="energy-saving-bulbs">Energy Saving Bulbs</h2>

Traditional, filament light bulbs use electricity flowing through a thin piece of wire called a filament. The filament gets hot and glows, producing light. As a lot of heat is also produced, filament bulbs are not very efficient.

Energy saving light bulbs do not use this method and are more efficient. This means that, for the same amount of electrical energy, the energy saving bulb will produce more light than the filament bulb.

<img src="/img/notes/01/light-bulb-2647226_960_720-175x300.png" alt="Power and Efficiency, figure 1" /></a>

<img src="/img/notes/01/download-2.jpg" alt="Power and Efficiency, figure 2" /></a>

Energy saving bulbs are usually more expensive to buy compared to filament bulbs. However, the energy saving bulb has a much longer lifetime than the filament bulb, which will need to be replaced regularly. Because the filament bulb is less efficient, the cost of electricity for the filament bulb will be much higher than the energy saving bulb. So, although the energy efficient bulb has a higher initial cost, it will save money in the long term.

<dl>
	<dt>A or B? Which of these devices uses the most energy? A - a 2kW heater used for 4 hours. B - a 3kW fire used for 3 hours.</dt>
	<dd id="Energy-Saving-Bulbs0" class="js-click-to-reveal">B</dd>
	<dt>A or B? Which of these devices uses the most energy? A - a 1kW iron used for 1 hours. B - a 2kW kettle used for 20 minutes.</dt>
	<dd id="Energy-Saving-Bulbs1" class="js-click-to-reveal">A</dd>
	<dt>An electric motor uses 275J to lift a load in 5s. What is the power of the motor? </dt>
	<dd id="Energy-Saving-Bulbs2" class="js-click-to-reveal">Your answer should include: 55W / 55</dd>
	<dt>What is the efficiency of a 60W lightbulb that produces 3W of light?</dt>
	<dd id="Energy-Saving-Bulbs3" class="js-click-to-reveal">0.05</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Power and Efficiency</h1>
</header>

<main class="blog-post__content">
	<h2 id="power">Power</h2>

	Power is the rate of using energy.

	Power is measured in Watts (W). 1W is 1J of energy being used per second.

	<a href="/img/notes/12/Capture.jpg" target="_blank"><img class="img-20" src="/img/notes/12/Capture.jpg" alt="Power and Efficiency, figure 1" /></a>

	A 100W light bulb will use more electrical energy than a 60W bulb if they are both on for the same length of time.

	You need to remember the equation for power for your exam:

	<h2 class="ql-align-center">P = E ÷ t</h2>

	P = power (W)

	E = work done or energy transferred (J)

	t = time (s)

	<a href="/img/notes/01/a.png" target="_blank"><img class="img-20" src="/img/notes/01/a.png" alt="Power and Efficiency, figure 2" /></a>

	There are also two other equations for power that you need to memorize which will be covered in more detail in the electricity lessons.

	Power = Current x Voltage

	<h2 class="ql-align-center">P = IV</h2>

	<a href="/img/notes/01/b.png" target="_blank"><img class="img-20" src="/img/notes/01/b.png" alt="Power and Efficiency, figure 3" /></a>

	And:

	Power = Current2 x Resistance

	<h2 class="ql-align-center">P = I2R</h2>

	<h2 id="converting-units">Converting Units</h2>

	It is important to be able to convert units as power is often given in kilowatts (kW).

	1 kW = 1000W

	To change W into kW, divide by 1000.

	To change kW into W, multiply by 1000.

	Worked Example

	<a href="/img/notes/01/d.png" target="_blank"><img class="img-20" src="/img/notes/01/d.png" alt="Power and Efficiency, figure 1" /></a>

	A weightlifter raises a bar from the floor to above his head. To lift the bar, the weightlifter does 5kJ of work in 2.5s.

	Calculate the power he produced:

	<ol>
		<li>Power = energy ÷ time</li>
		<li>5kJ = 5000J</li>
		<li>Power = 5000 ÷ 2.5 = 2000 W</li>
	</ol>

	Another weightlifter lifts the same weight in a shorter time. Compare the power of the two weightlifters.

	<ol>
		<li>Using the same amount of energy in a shorter time would require more power</li>
	</ol>

	<h2 id="sankey-diagrams">Sankey Diagrams</h2>

	Sankey diagrams were introduced in a previous lesson. They can be used to calculate efficiency.

	<a href="/img/notes/12/3.jpg" target="_blank"><img class="img-20" src="/img/notes/12/3.jpg" alt="Power and Efficiency, figure 1" /></a>

	For this Sankey diagram, the useful energy output is 10J and the total energy input is 60J. Therefore, the efficiency is 10÷60=0.17 (or 17%)

	<h2 id="efficiency">Efficiency</h2>

	All devices waste some energy, usually as heat due to friction between moving parts.

	<ol>
		<li>For example, a light bulb is designed to produce light, but also produces heat energy which is dissipated into the surroundings.</li>
		<li>A car engine is designed to produce kinetic energy but also produces heat and sound which is dissipated into the surroundings.</li>
	</ol>

	Efficiency is a measurement of how much energy is converted usefully (compared to how much is wasted).

	You need to remember the equations for efficiency:

	<h2 class="ql-align-center">Efficiency = useful energy out ÷ total energy in</h2>

	Or

	<h2 class="ql-align-center">Efficiency = useful power out ÷ total power in</h2>

	Efficiency has no units!

	It can be written as a number between 0 and 1 or as a %. For example, an efficiency of 0.25 is the same as an efficiency of 25%.

	Because some energy is always wasted from every device, efficiency should always be less than 1 or less than 100%. If you get an answer that is bigger than 1 or 100%, you have made a mistake somewhere in your calculation!

	Worked Examples

	<a href="/img/notes/01/drill-1295561_960_720-290x300.png" target="_blank"><img class="img-20" src="/img/notes/01/drill-1295561_960_720-290x300.png" alt="Power and Efficiency, figure 1" /></a>

	A power drill uses 500J of electricity. Only 400J of kinetic energy was generated by the drill. What is its efficiency?

	<ol>
		<li>Efficiency = useful energy out ÷ total energy in</li>
		<li>Efficiency = 400 ÷ 500</li>
		<li>Efficiency = 0.8 (or 80%)</li>
	</ol>

	<a href="/img/notes/12/Capture2.jpg" target="_blank"><img class="img-20" src="/img/notes/12/Capture2.jpg" alt="Power and Efficiency, figure 2" /></a>

	A portable speaker converts 150J of electrical energy into 30J of sound energy. Calculate its efficiency.

	<ol>
		<li>Efficiency = useful energy out ÷ total energy in</li>
		<li>Efficiency = 30 ÷ 150</li>
		<li>Efficiency = 0.2 (or 20%)</li>
	</ol>

	<h2 id="energy-saving-bulbs">Energy Saving Bulbs</h2>

	Traditional, filament light bulbs use electricity flowing through a thin piece of wire called a filament. The filament gets hot and glows, producing light. As a lot of heat is also produced, filament bulbs are not very efficient.

	Energy-saving light bulbs do not use this method and are more efficient. This means that, for the same amount of electrical energy, the energy-saving bulb will produce more light than the filament bulb.

	<a href="/img/notes/01/light-bulb-2647226_960_720-175x300.png" target="_blank"><img class="img-20" src="/img/notes/01/light-bulb-2647226_960_720-175x300.png" alt="Power and Efficiency, figure 1" /></a>

	<a href="/img/notes/01/download-2.jpg" target="_blank"><img class="img-20" src="/img/notes/01/download-2.jpg" alt="Power and Efficiency, figure 2" /></a>

	Energy-saving bulbs are usually more expensive to buy compared to filament bulbs. However, the energy-saving bulb has a much longer lifetime than the filament bulb, which will need to be replaced regularly. Because the filament bulb is less efficient, the cost of electricity for the filament bulb will be much higher than the energy-saving bulb. So, although the energy-efficient bulb has a higher initial cost, it will save money in the long term.

	<dl>
		<dt>A or B? Which of these devices uses the most energy? A - a 2kW heater used for 4 hours. B - a 3kW fire used for 3 hours.</dt>
		<dd id="Energy-Saving-Bulbs0" class="js-click-to-reveal">B</dd>
		<dt>A or B? Which of these devices uses the most energy? A - a 1kW iron used for 1 hour. B - a 2kW kettle used for 20 minutes.</dt>
		<dd id="Energy-Saving-Bulbs1" class="js-click-to-reveal">A</dd>
		<dt>An electric motor uses 275J to lift a load in 5s. What is the power of the motor? </dt>
		<dd id="Energy-Saving-Bulbs2" class="js-click-to-reveal">Your answer should include: 55W / 55</dd>
		<dt>What is the efficiency of a 60W light bulb that produces 3W of light?</dt>
		<dd id="Energy-Saving-Bulbs3" class="js-click-to-reveal">0.05</dd>
	</dl>
</main>

physics

Power and Efficiency

Energy

<header>
			<h1 class="blog-post__title">Thermal Energy</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="heat-transfer">Heat Transfer</h2>

<img src="/img/notes/01/1-1.png" alt="Thermal Energy, figure 1" /></a>

<ol>
 <li>Thermal energy (heat) transfer happens when there is a difference in temperature</li>
 <li>The energy moves from the higher temperature area to the lower temperature area</li>
 <li>Conduction</li>
 <li>Convection</li>
 <li>Radiation</li>
</ol>

<h2 id="conduction">Conduction</h2>

Conduction is how thermal energy travels through solids.

<img src="/img/notes/01/2.png" alt="Thermal Energy, figure 1" /></a>

In a solid, the particles are tightly packed together in fixed positions.

<img src="/img/notes/01/ezgif.com-resize.gif" alt="Thermal Energy, figure 2" /></a>

<ol>
 <li>The particles are close together, vibrating in fixed positions</li>
 <li>As the solid is heated, thermal energy is transferred into kinetic energy in the particles.</li>
 <li>The particles vibrate faster</li>
 <li>The energy/vibrations are passed on from particle to particle</li>
 <li>Heat spreads through the solid</li>
</ol>

<img src="/img/notes/01/4.png" alt="Thermal Energy, figure 3" /></a>

When you hold ice in your hand:

<ol>
 <li>Thermal energy moves from your hand to the ice</li>
 <li>Particle vibrations are passed from one particle to the next</li>
 <li>As your skin is losing thermal energy, it feels cold</li>
</ol>

Metals are good conductors of electricity. As well as vibrations being passed from particle to particle, as described above, metals also have ‘free’ electrons that can carry energy through the solid. This means that thermal energy conducts faster through metals than other materials.

<h2 id="insulation">Insulation</h2>

<ol>
 <li>Air is a poor conductor of heat as there are large distances between the particles</li>
 <li>This can be used to prevent heat loss from objects</li>
</ol>

<h2 id="required-practical--insulation">Required Practical – Insulation</h2>

You need to be familiar with the practical method used to investigate the effectiveness of insulating materials.

<img src="/img/notes/01/5.png" alt="Thermal Energy, figure 1" /></a>

<ol>
 <li>Hot water is placed in a container with a thermometer</li>
 <li>Insulating material is wrapped around the container</li>
 <li>The type of material, or different thicknesses of a particular material can be investigated</li>
 <li>The temperature is recorded over a period of time.</li>
 <li>The temperature change for different materials/thicknesses can be compared</li>
</ol>

Potential errors in this investigation include:

<ol>
 <li>Different starting temperatures of water can lead to different rates of heat loss each time</li>
 <li>Heat can be lost through the top/bottom of the container</li>
 <li>Random error can occur when reading the thermometer</li>
</ol>

<h2 id="specific-heat-capacity">Specific Heat Capacity</h2>

<img src="/img/notes/01/6.png" alt="Thermal Energy, figure 1" /></a>

The temperature change of a substance depends on the following factors:

<ol>
 <li>The amount of thermal energy supplied</li>
 <li>The mass of the substance</li>
 <li>What the substance is</li>
</ol>

Different substances absorb thermal energy at different rates.

The specific heat capacity of a substance is the energy needed to raise the temperature of 1kg of the substance by 1oC

<h3 class="ql-align-center">∆E = mc∆θ</h3>

∆E = energy transferred (J)

m = mass (kg)

c = specific heat capacity (J/kgoC)

∆θ = temperature change (oC)

(you will be given this equation on a data sheet in the exam)

Worked Example

0.15 kg of ice cream mixture was cooled from room temperature (20 °C) to 0°C. This required 6000 J of energy. What is the specific heat capacity of this ice cream?

Rearrange: c = ∆E ÷ (m∆θ)

c = 6000 ÷ (0.15x20)

c = 2000 J/kgoC

<h2 id="storage-heater">Storage Heater</h2>

A storage heater uses electricity at night (when it is cheaper) to heat bricks or concrete blocks inside the heater.

<img src="/img/notes/01/7.png" alt="Thermal Energy, figure 1" /></a>

The bricks have a high specific heat capacity so they warm up slowly and then cool down slowly during the day, releasing thermal energy into the room. This is cheaper than using hot water in radiators but offers less control over the temperature of the room.

<h2 id="required-practical--specific-heat-capacity">Required Practical – Specific Heat Capacity</h2>

You need to be familiar with the practical procedure used to find the specific heat capacity of a given material.

<img src="/img/notes/01/8.png" alt="Thermal Energy, figure 1" /></a>

<ol>
 <li>Measure the mass of the aluminium block (or other material)</li>
 <li>Insert thermometer and record the temperature of the block (before heating starts)</li>
 <li>Use an immersion heater to heat the block for a certain amount of time</li>
 <li>The immersion heater should be connected to a joulemeter and the amount of energy supplied to the heater should be recorded</li>
 <li>Measure the temperature of the block after heating and calculate the temperature change</li>
 <li>Use the values recorded in your investigation to calculate the specific heat capacity</li>
 <li>Specific heat capacity = energy transferred ÷ (mass x temperature change)</li>
</ol>

The value you calculate for specific heat capacity is unlikely to be exactly the same as the published values for the same material.

This is due to errors in the investigation, including:

<ol>
 <li>The Joulemeter measures the electrical energy supplied to the heater. Not all of this energy will be transferred as thermal energy to the block – some will be lost to the atmosphere.</li>
 <li>Heat may be lost form the block to the surroundings during the experiment, this can be improved by insulating the block.</li>
 <li>Random error in reading the thermometer or balance</li>
</ol>

<dl>
	<dt>What is the name for heat transfer in solids?</dt>
	<dd id="Required-Practical-Specific-Heat-Capacity0" class="js-click-to-reveal">conduction</dd>
	<dt>When a substance is heated, thermal energy is transferred to which type of energy in the particles?</dt>
	<dd id="Required-Practical-Specific-Heat-Capacity1" class="js-click-to-reveal">kinetic</dd>
	<dt>The temperature change of an object depends on the material, the thermal energy supplied and which other variable?</dt>
	<dd id="Required-Practical-Specific-Heat-Capacity2" class="js-click-to-reveal">mass</dd>
	<dt>What is the name for a material which does not conduct thermal energy very well?</dt>
	<dd id="Required-Practical-Specific-Heat-Capacity3" class="js-click-to-reveal">insulator</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Thermal Energy</h1>
</header>

<main class="blog-post__content">
	<h2 id="heat-transfer">Heat Transfer</h2>

	<a href="/img/notes/01/1-1.png" target="_blank"><img src="/img/notes/01/1-1.png" alt="Thermal Energy, figure 1" /></a>

	<ol>
		<li>Thermal energy (heat) transfer happens when there is a difference in temperature.</li>
		<li>The energy moves from the higher temperature area to the lower temperature area.</li>
		<li>Conduction.</li>
		<li>Convection.</li>
		<li>Radiation.</li>
	</ol>

	<h2 id="conduction">Conduction</h2>

	Conduction is how thermal energy travels through solids.

	<a href="/img/notes/01/2.png" target="_blank"><img src="/img/notes/01/2.png" alt="Thermal Energy, figure 1" /></a>

	In a solid, the particles are tightly packed together in fixed positions.

	<a href="/img/notes/01/ezgif.com-resize.gif" target="_blank"><img src="/img/notes/01/ezgif.com-resize.gif" alt="Thermal Energy, figure 2" /></a>

	<ol>
		<li>The particles are close together, vibrating in fixed positions.</li>
		<li>As the solid is heated, thermal energy is transferred into kinetic energy in the particles.</li>
		<li>The particles vibrate faster.</li>
		<li>The energy/vibrations are passed on from particle to particle.</li>
		<li>Heat spreads through the solid.</li>
	</ol>

	<a href="/img/notes/01/4.png" target="_blank"><img src="/img/notes/01/4.png" alt="Thermal Energy, figure 3" /></a>

	When you hold ice in your hand:

	<ol>
		<li>Thermal energy moves from your hand to the ice.</li>
		<li>Particle vibrations are passed from one particle to the next.</li>
		<li>As your skin is losing thermal energy, it feels cold.</li>
	</ol>

	Metals are good conductors of electricity. As well as vibrations being passed from particle to particle, as described above, metals also have ‘free’ electrons that can carry energy through the solid. This means that thermal energy conducts faster through metals than other materials.

	<h2 id="insulation">Insulation</h2>

	<ol>
		<li>Air is a poor conductor of heat as there are large distances between the particles.</li>
		<li>This can be used to prevent heat loss from objects.</li>
	</ol>

	<h2 id="required-practical--insulation">Required Practical – Insulation</h2>

	You need to be familiar with the practical method used to investigate the effectiveness of insulating materials.

	<a href="/img/notes/01/5.png" target="_blank"><img src="/img/notes/01/5.png" alt="Thermal Energy, figure 1" /></a>

	<ol>
		<li>Hot water is placed in a container with a thermometer.</li>
		<li>Insulating material is wrapped around the container.</li>
		<li>The type of material, or different thicknesses of a particular material can be investigated.</li>
		<li>The temperature is recorded over a period of time.</li>
		<li>The temperature change for different materials/thicknesses can be compared.</li>
	</ol>

	Potential errors in this investigation include:

	<ol>
		<li>Different starting temperatures of water can lead to different rates of heat loss each time.</li>
		<li>Heat can be lost through the top/bottom of the container.</li>
		<li>Random error can occur when reading the thermometer.</li>
	</ol>

	<h2 id="specific-heat-capacity">Specific Heat Capacity</h2>

	The temperature change of a substance depends on the following factors:

	<ol>
		<li>The amount of thermal energy supplied.</li>
		<li>The mass of the substance.</li>
		<li>What the substance is.</li>
	</ol>

	Different substances absorb thermal energy at different rates.

	The specific heat capacity of a substance is the energy needed to raise the temperature of 1kg of the substance by 1oC.

	<h3 class="ql-align-center">∆E = mc∆θ</h3>

	∆E = energy transferred (J).

	m = mass (kg).

	c = specific heat capacity (J/kgoC).

	∆θ = temperature change (oC).

	(You will be given this equation on a data sheet in the exam.)

	Worked Example:

	0.15 kg of ice cream mixture was cooled from room temperature (20 °C) to 0°C. This required 6000 J of energy. What is the specific heat capacity of this ice cream?

	Rearrange: c = ∆E ÷ (m∆θ).

	c = 6000 ÷ (0.15x20).

	c = 2000 J/kgoC.

	<h2 id="storage-heater">Storage Heater</h2>

	A storage heater uses electricity at night (when it is cheaper) to heat bricks or concrete blocks inside the heater.

	<a href="/img/notes/01/7.png" target="_blank"><img src="/img/notes/01/7.png" alt="Thermal Energy, figure 1" /></a>

	The bricks have a high specific heat capacity so they warm up slowly and then cool down slowly during the day, releasing thermal energy into the room. This is cheaper than using hot water in radiators but offers less control over the temperature of the room.

	<h2 id="required-practical--specific-heat-capacity">Required Practical – Specific Heat Capacity</h2>

	You need to be familiar with the practical procedure used to find the specific heat capacity of a given material.

	<a href="/img/notes/01/8.png" target="_blank"><img src="/img/notes/01/8.png" alt="Thermal Energy, figure 1" /></a>

	<ol>
		<li>Measure the mass of the aluminium block (or other material).</li>
		<li>Insert thermometer and record the temperature of the block (before heating starts).</li>
		<li>Use an immersion heater to heat the block for a certain amount of time.</li>
		<li>The immersion heater should be connected to a joulemeter and the amount of energy supplied to the heater should be recorded.</li>
		<li>Measure the temperature of the block after heating and calculate the temperature change.</li>
		<li>Use the values recorded in your investigation to calculate the specific heat capacity.</li>
		<li>Specific heat capacity = energy transferred ÷ (mass x temperature change).</li>
	</ol>

	The value you calculate for specific heat capacity is unlikely to be exactly the same as the published values for the same material.

	This is due to errors in the investigation, including:

	<ol>
		<li>The Joulemeter measures the electrical energy supplied to the heater. Not all of this energy will be transferred as thermal energy to the block – some will be lost to the atmosphere.</li>
		<li>Heat may be lost from the block to the surroundings during the experiment, this can be improved by insulating the block.</li>
		<li>Random error in reading the thermometer or balance.</li>
	</ol>

	<dl>
		<dt>What is the name for heat transfer in solids?</dt>
		<dd id="Required-Practical-Specific-Heat-Capacity0" class="js-click-to-reveal">Conduction.</dd>
		<dt>When a substance is heated, thermal energy is transferred to which type of energy in the particles?</dt>
		<dd id="Required-Practical-Specific-Heat-Capacity1" class="js-click-to-reveal">Kinetic.</dd>
		<dt>The temperature change of an object depends on the material, the thermal energy supplied, and which other variable?</dt>
		<dd id="Required-Practical-Specific-Heat-Capacity2" class="js-click-to-reveal">Mass.</dd>
		<dt>What is the name for a material which does not conduct thermal energy very well?</dt>
		<dd id="Required-Practical-Specific-Heat-Capacity3" class="js-click-to-reveal">Insulator.</dd>
	</dl>
</main>

Thermal Energy

<header>
			<h1 class="blog-post__title">Energy Resources</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="energy-resources">Energy Resources</h2>

Energy Resources can be classified as renewable or non-renewable.

Non-renewable energy resources will eventually run out (for example: coal, oil and gas)

Renewable energy resources will not run out (for example wind and solar power)

<h2 id="renewable-energy-resources">Renewable Energy Resources</h2>

Renewable energy resources include:

<ol>
 <li>Hydroelectric</li>
 <li>Wind</li>
 <li>Solar</li>
 <li>Tidal</li>
 <li>Wave</li>
 <li>Geothermal</li>
 <li>Biomass</li>
</ol>

<h3 id="hydroelectric">Hydroelectric</h3>

<img src="/img/notes/02/2000px-Hydroelectric_dam.svg-1024x695.png" alt="Energy Resources, figure 1" /></a>

Hydroelectric generators use moving water to drive turbines. Large scale hydroelectric power stations usually create a reservoir of water by building a dam. The water can then be released past turbines to generate electricity.

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>Cheap to run</li>
 <li>Renewable</li>
</ol>

Disadvantages:

<ol>
 <li>Limited locations are suitable as there needs to be a supply of water and enough land to create a reservoir</li>
 <li>Building a dam and reservoir has an impact on the local environment (i.e. animal habitats, farmland)</li>
</ol>

<h3 id="wind">Wind</h3>

<img src="/img/notes/02/ezgif.com-resize-1.gif" alt="Energy Resources, figure 2" /></a>

Wind turbines use the kinetic energy of the wind to generate electricity.

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>No fuel costs</li>
 <li>Renewable</li>
</ol>

Disadvantages:

<ol>
 <li>Low power output from each turbine so lots of turbines are needed</li>
 <li>Unreliable supply – they only work when it is windy</li>
 <li>Visual pollution – some people think that they spoil the landscape</li>
</ol>

<h3 id="solar">Solar</h3>

<img src="/img/notes/02/Solar_panels_on_a_roof-1024x520.jpg" alt="Energy Resources, figure 3" /></a>

Solar (photovoltaic) cells convert sunlight to electricity.

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>No fuel costs</li>
</ol>

Disadvantages:

<ol>
 <li>Expensive to produce the panels</li>
 <li>Low power output</li>
 <li>Unreliable supply – they do not work at night</li>
</ol>

Solar energy can also be used by solar heating panels to heat water that can be used to keep a building warm, rather than generating electricity.

<h3 id="geothermal">Geothermal</h3>

<img src="/img/notes/02/Geothermal-energy.png" alt="Energy Resources, figure 4" /></a>

Geothermal uses the heat that is naturally occurring below the surface of the Earth. Water can be pumped down into the Earth’s crust where it is heated up. The steam produced can be used to drive a turbine and generate electricity at the surface.

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>No fuel costs</li>
</ol>

Disadvantages:

<ol>
 <li>Expensive to build</li>
 <li>Only suitable in areas with the right geological conditions</li>
</ol>

<h3 id="wave">Wave</h3>

<img src="/img/notes/02/Wave_float_with_piston_rod.gif" alt="Energy Resources, figure 5" /></a>

The motion of waves in the sea can be used to turn turbines and generate electricity.

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>No fuel costs</li>
</ol>

Disadvantages:

<ol>
 <li>Only suitable for use in coastal areas</li>
 <li>Installing the turbines and generators can interfere with other coastal activities (fishing, swimming etc) and/or wildlife</li>
</ol>

<h3 id="tidal">Tidal</h3>

<img src="/img/notes/02/Sihwa_Lake_Tidal_Power_Station_01.png" alt="Energy Resources, figure 6" /></a>

At the coast, the water level (tide) rises and falls twice a day due to the moon’s gravitational field. As the water moves in/out from the coastline, turbines can be used to generate electricity.

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>No fuel costs</li>
</ol>

Disadvantages:

<ol>
 <li>Only suitable for use in coastal areas</li>
 <li>Installing the turbines and generators can interfere with other coastal activities (fishing, swimming etc) and/or wildlife</li>
</ol>

<h3 id="biofuels">Biofuels</h3>

Biofuels are made from living or recently living organisms. Examples include: methane from animal waste, rapeseed oil, ethanol from sugar cane, woodchips

Advantages:

<ol>
 <li>Renewable (as long as the source is replaced at the same rate it is used)</li>
 <li>Suitable for use in remote/rural locations</li>
 <li>Carbon neutral - the amount of carbon taken into the organism when it living should equal the amount of carbon given out when it is burned</li>
</ol>

Disadvantages:

<ol>
 <li>Biofuels release carbon dioxide when burned.</li>
 <li>Low power output – only suitable for small scale use</li>
</ol>

<h2 id="non-renewable-energy-resources">Non-Renewable Energy Resources</h2>

Fossil Fuels

Coal, oil and gas are fossil fuels. They have been formed underground from the remains of ancient organisms over millions of years.

<img src="/img/notes/02/2000px-Coal_fired_power_plant_diagram.svg-1024x635.png" alt="Energy Resources, figure 1" /></a>

A power station can burn a fossil fuel to heat water, producing steam. The steam is used to turn a turbine which turns a generator, producing electricity.

Advantages:

<ol>
 <li>Fossil fuel power stations generate a high power output</li>
</ol>

Disadvantages:

<ol>
 <li>Non renewable</li>
 <li>Carbon dioxide (and other pollutants) released into the atmosphere when burned</li>
 <li>Large amounts of fuel needed</li>
</ol>

Nuclear Power﻿

<img src="/img/notes/02/320px-PWR_nuclear_power_plant_diagram.svg.png" alt="Energy Resources, figure 2" /></a>

Nuclear power stations use the process of nuclear fission. Splitting a nucleus of uranium in the reactor generates large amounts of energy. This heat is used to produce steam. The steam is used to turn a turbine which turns a generator, producing electricity.

Advantages:

<ol>
 <li>No waste gases produced</li>
 <li>Large power output from only a small amount of fuel</li>
</ol>

Disadvantages:

<ol>
 <li>Radioactive waste produced</li>
 <li>Power stations are expensive to build and decommission</li>
</ol>

<h2 id="evaluating-energy-resources">Evaluating Energy Resources</h2>

When evaluating and comparing energy resources, consider the following factors:

<ol>
 <li>Running Costs – includes fuel, transport, staff, maintenance</li>
 <li>Lifecycle costs – building, decommissioning</li>
 <li>Power Output</li>
 <li>Environmental Impact</li>
 <li>Efficiency</li>
 <li>Renewable/Non-renewable</li>
</ol>

Worked Example

Compare the advantages and disadvantages of using fossil fuels and nuclear power to provide electricity to the UK:

Fossil Fuels

Advantages:

<ol>
 <li>Quicker/cheaper to build the power station</li>
 <li>Can respond quickly to changes in demand</li>
 <li>Can be built anywhere</li>
</ol>

Disadvantages:

<ol>
 <li>Carbon dioxide produced (contributing to climate change)</li>
 <li>Non-renewable</li>
 <li>Acid rain</li>
</ol>

Nuclear

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>Small amounts of fuel needed</li>
 <li>Smaller running costs</li>
 <li>More plentiful supply (although not renewable)</li>
</ol>

Disadvantages:

<ol>
 <li>Radioactive waste</li>
 <li>Expensive/slower to build and decommission</li>
 <li>Local public may not want it built in their location</li>
</ol>

<dl>
	<dt>In a power station, steam is often used to turn a __________?</dt>
	<dd id="Evaluating-Energy-Resources0" class="js-click-to-reveal">turbine</dd>
	<dt>What is the name for the category of fuels made from living or recently living organisms?</dt>
	<dd id="Evaluating-Energy-Resources1" class="js-click-to-reveal">Your answer should include: biofuels / biofuel</dd>
	<dt>What is the name of the energy resource that uses a dam to cause water to flow past turbines to generate electricity?</dt>
	<dd id="Evaluating-Energy-Resources2" class="js-click-to-reveal">hydroelectric</dd>
	<dt>What is the name of the energy resource that uses heat that occurs below the Earth's surface?</dt>
	<dd id="Evaluating-Energy-Resources3" class="js-click-to-reveal">geothermal</dd>
	<dt>Coal, oil and gas are known as _______ fuels.</dt>
	<dd id="Evaluating-Energy-Resources4" class="js-click-to-reveal">fossil</dd>
</dl>


		</main>

<header>
			<h1 class="blog-post__title">Energy Resources</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="energy-resources">Energy Resources</h2>

Energy resources can be classified as renewable or non-renewable.

Non-renewable energy resources will eventually run out (for example: coal, oil, and gas).

Renewable energy resources will not run out (for example, wind and solar power).

<h2 id="renewable-energy-resources">Renewable Energy Resources</h2>

Renewable energy resources include:

<ol>
 <li>Hydroelectric</li>
 <li>Wind</li>
 <li>Solar</li>
 <li>Tidal</li>
 <li>Wave</li>
 <li>Geothermal</li>
 <li>Biomass</li>
</ol>

<h3 id="hydroelectric">Hydroelectric</h3>

<a href="/img/notes/02/2000px-Hydroelectric_dam.svg-1024x695.png" target="_blank"><img src="/img/notes/02/2000px-Hydroelectric_dam.svg-1024x695.png" alt="Energy Resources, figure 1" /></a>

Hydroelectric generators use moving water to drive turbines. Large-scale hydroelectric power stations usually create a reservoir of water by building a dam. The water can then be released past turbines to generate electricity.

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>Cheap to run</li>
 <li>Renewable</li>
</ol>

Disadvantages:

<ol>
 <li>Limited locations are suitable as there needs to be a supply of water and enough land to create a reservoir</li>
 <li>Building a dam and reservoir has an impact on the local environment (i.e., animal habitats, farmland)</li>
</ol>

<h3 id="wind">Wind</h3>

<a href="/img/notes/02/ezgif.com-resize-1.gif" target="_blank"><img src="/img/notes/02/ezgif.com-resize-1.gif" alt="Energy Resources, figure 2" /></a>

Wind turbines use the kinetic energy of the wind to generate electricity.

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>No fuel costs</li>
 <li>Renewable</li>
</ol>

Disadvantages:

<ol>
 <li>Low power output from each turbine, so lots of turbines are needed</li>
 <li>Unreliable supply – they only work when it is windy</li>
 <li>Visual pollution – some people think that they spoil the landscape</li>
</ol>

<h3 id="solar">Solar</h3>

<a href="/img/notes/02/Solar_panels_on_a_roof-1024x520.jpg" target="_blank"><img src="/img/notes/02/Solar_panels_on_a_roof-1024x520.jpg" alt="Energy Resources, figure 3" /></a>

Solar (photovoltaic) cells convert sunlight to electricity.

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>No fuel costs</li>
</ol>

Disadvantages:

<ol>
 <li>Expensive to produce the panels</li>
 <li>Low power output</li>
 <li>Unreliable supply – they do not work at night</li>
</ol>

Solar energy can also be used by solar heating panels to heat water that can be used to keep a building warm, rather than generating electricity.

<h3 id="geothermal">Geothermal</h3>

<a href="/img/notes/02/Geothermal-energy.png" target="_blank"><img src="/img/notes/02/Geothermal-energy.png" alt="Energy Resources, figure 4" /></a>

Geothermal uses the heat that is naturally occurring below the surface of the Earth. Water can be pumped down into the Earth’s crust where it is heated up. The steam produced can be used to drive a turbine and generate electricity at the surface.

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>No fuel costs</li>
</ol>

Disadvantages:

<ol>
 <li>Expensive to build</li>
 <li>Only suitable in areas with the right geological conditions</li>
</ol>

<h3 id="wave">Wave</h3>

<a href="/img/notes/02/Wave_float_with_piston_rod.gif" target="_blank"><img src="/img/notes/02/Wave_float_with_piston_rod.gif" alt="Energy Resources, figure 5" /></a>

The motion of waves in the sea can be used to turn turbines and generate electricity.

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>No fuel costs</li>
</ol>

Disadvantages:

<ol>
 <li>Only suitable for use in coastal areas</li>
 <li>Installing the turbines and generators can interfere with other coastal activities (fishing, swimming, etc.) and/or wildlife</li>
</ol>

<h3 id="tidal">Tidal</h3>

<a href="/img/notes/02/Sihwa_Lake_Tidal_Power_Station_01.png" target="_blank"><img src="/img/notes/02/Sihwa_Lake_Tidal_Power_Station_01.png" alt="Energy Resources, figure 6" /></a>

At the coast, the water level (tide) rises and falls twice a day due to the moon’s gravitational field. As the water moves in/out from the coastline, turbines can be used to generate electricity.

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>No fuel costs</li>
</ol>

Disadvantages:

<ol>
 <li>Only suitable for use in coastal areas</li>
 <li>Installing the turbines and generators can interfere with other coastal activities (fishing, swimming, etc.) and/or wildlife</li>
</ol>

<h3 id="biofuels">Biofuels</h3>

Biofuels are made from living or recently living organisms. Examples include methane from animal waste, rapeseed oil, ethanol from sugar cane, woodchips.

Advantages:

<ol>
 <li>Renewable (as long as the source is replaced at the same rate it is used)</li>
 <li>Suitable for use in remote/rural locations</li>
 <li>Carbon neutral - the amount of carbon taken into the organism when it is living should equal the amount of carbon given out when it is burned</li>
</ol>

Disadvantages:

<ol>
 <li>Biofuels release carbon dioxide when burned.</li>
 <li>Low power output – only suitable for small-scale use</li>
</ol>

<h2 id="non-renewable-energy-resources">Non-Renewable Energy Resources</h2>

Fossil Fuels

Coal, oil, and gas are fossil fuels. They have been formed underground from the remains of ancient organisms over millions of years.

<a href="/img/notes/02/2000px-Coal_fired_power_plant_diagram.svg-1024x635.png" target="_blank"><img src="/img/notes/02/2000px-Coal_fired_power_plant_diagram.svg-1024x635.png" alt="Energy Resources, figure 1" /></a>

A power station can burn a fossil fuel to heat water, producing steam. The steam is used to turn a turbine, which turns a generator, producing electricity.

Advantages:

<ol>
 <li>Fossil fuel power stations generate a high power output</li>
</ol>

Disadvantages:

<ol>
 <li>Non-renewable</li>
 <li>Carbon dioxide (and other pollutants) released into the atmosphere when burned</li>
 <li>Large amounts of fuel needed</li>
</ol>

Nuclear Power

<a href="/img/notes/02/320px-PWR_nuclear_power_plant_diagram.svg.png" target="_blank"><img src="/img/notes/02/320px-PWR_nuclear_power_plant_diagram.svg.png" alt="Energy Resources, figure 2" /></a>

Nuclear power stations use the process of nuclear fission. Splitting a nucleus of uranium in the reactor generates large amounts of energy. This heat is used to produce steam. The steam is used to turn a turbine, which turns a generator, producing electricity.

Advantages:

<ol>
 <li>No waste gases produced</li>
 <li>Large power output from only a small amount of fuel</li>
</ol>

Disadvantages:

<ol>
 <li>Radioactive waste produced</li>
 <li>Power stations are expensive to build and decommission</li>
</ol>

<h2 id="evaluating-energy-resources">Evaluating Energy Resources</h2>

When evaluating and comparing energy resources, consider the following factors:

<ol>
 <li>Running Costs – includes fuel, transport, staff, maintenance</li>
 <li>Lifecycle costs – building, decommissioning</li>
 <li>Power Output</li>
 <li>Environmental Impact</li>
 <li>Efficiency</li>
 <li>Renewable/Non-renewable</li>
</ol>

Worked Example

Compare the advantages and disadvantages of using fossil fuels and nuclear power to provide electricity to the UK:

Fossil Fuels

Advantages:

<ol>
 <li>Quicker/cheaper to build the power station</li>
 <li>Can respond quickly to changes in demand</li>
 <li>Can be built anywhere</li>
</ol>

Disadvantages:

<ol>
 <li>Carbon dioxide produced (contributing to climate change)</li>
 <li>Non-renewable</li>
 <li>Acid rain</li>
</ol>

Nuclear

Advantages:

<ol>
 <li>No gas emissions</li>
 <li>Small amounts of fuel needed</li>
 <li>Smaller running costs</li>
 <li>More plentiful supply (although not renewable)</li>
</ol>

Disadvantages:

<ol>
 <li>Radioactive waste</li>
 <li>Expensive/slower to build and decommission</li>
 <li>Local public may not want it built in their location</li>
</ol>

<dl>
	<dt>In a power station, steam is often used to turn a __________?</dt>
	<dd id="Evaluating-Energy-Resources0" class="js-click-to-reveal">turbine</dd>
	<dt>What is the name for the category of fuels made from living or recently living organisms?</dt>
	<dd id="Evaluating-Energy-Resources1" class="js-click-to-reveal">Your answer should include: biofuels / biofuel</dd>
	<dt>What is the name of the energy resource that uses a dam to cause water to flow past turbines to generate electricity?</dt>
	<dd id="Evaluating-Energy-Resources2" class="js-click-to-reveal">hydroelectric</dd>
	<dt>What is the name of the energy resource that uses heat that occurs below the Earth's surface?</dt>
	<dd id="Evaluating-Energy-Resources3" class="js-click-to-reveal">geothermal</dd>
	<dt>Coal, oil, and gas are known as _______ fuels.</dt>
	<dd id="Evaluating-Energy-Resources4" class="js-click-to-reveal">fossil</dd>
</dl>


		</main>

Energy Resources

<header>
			<h1 class="blog-post__title">Energy Transfer</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="energy-transfer">Energy Transfer</h2>

Energy exists in different forms (stores) and is transferred from one store to another.

Examples of energy stores:

<ol>
 <li>Light</li>
 <li>Sound</li>
 <li>Heat</li>
 <li>Chemical</li>
 <li>Electrical</li>
 <li>Kinetic (movement)</li>
 <li>Gravitational Potential (Stored by objects at a height)</li>
 <li>Elastic Potential (Stored by elastic materials)</li>
</ol>

Energy Transfer

Devices transfer energy from one store (form) into another.

<img src="/img/notes/12/Capture.jpg" alt="Energy Transfer, figure 1" /></a><img src="/img/notes/12/Capture2.jpg" alt="Energy Transfer, figure 2" /></a>

<ol>
 <li>A light bulb converts electrical energy into light</li>
 <li>A loudspeaker converts electrical energy into sound</li>
</ol>

<h2 id="sankey-diagrams">Sankey Diagrams</h2>

A Sankey diagram shows the energy transfers for a particular device.

<ol>
 <li>The energy supplied is shown at the start of the arrow</li>
 <li>The useful energy is shown by the arrow pointing straight ahead</li>
 <li>‘Wasted’ energy is shown by the arrow curving away from the useful energy</li>
</ol>

The size of the arrows represents the amount of energy.

<img src="/img/notes/12/3.jpg" alt="Energy Transfer, figure 1" /></a>

Example Sankey Diagrams:

<img src="/img/notes/12/4.jpg" alt="Energy Transfer, figure 2" /></a><img src="/img/notes/12/5.jpg" alt="Energy Transfer, figure 3" /></a><img src="/img/notes/12/6.jpg" alt="Energy Transfer, figure 4" /></a>

<h2 id="elastic-potential-energy">Elastic Potential Energy</h2>

Elastic Potential Energy (EPE) is stored in elastic materials when they are stretched or squashed. The EPE causes them to move back to their original shape when released.

For example:

<img src="/img/notes/12/Screen-Shot-2018-01-25-at-20.51.30.png" alt="Energy Transfer, figure 1" /></a>

<ol>
 <li>Energy is used to stretch a catapult</li>
 <li>EPE is stored in the the catapult while it is stretched</li>
 <li>EPE released (transformed into Kinetic Energy) when the catapult is released, causing the object to move forward</li>
</ol>

Elastic Potential Energy can be calculated using the following equation (you do NOT need to memorise this equation)

EPE = (ke2)÷2

__EPE __= Elastic Potential Energy (J)

K = spring constant (N/m)

e = extension (m)

Worked Example 1

Calculate the EPE stored in a spring with spring constant 250N/m when it is stretched to extend by 0.2m

EPE=ke2÷2

EPE=250 x 0.22÷2

EPE= 5J

Worked Example 2

If a spring with spring constant 300N/m has 20J of EPE, how much has it extended?

e= √(2EPE÷ k)

e= √(2x20÷ 300)

e= 0.37m

<h2 id="kinetic-energy">Kinetic Energy</h2>

Kinetic energy is the energy possessed by a moving object. It depends on the velocity (speed) of the object and the mass of the object.

Kinetic Energy can be calculated using this equation: (you DO need to memorise this equation)

KE = (mv2)÷2

KE = Kinetic Energy (J)

m = mass (kg)

v = velocity (m/s)

Rearranging this equation to find velocity can be a bit tricky!

V = √(2KE ÷ m)

Worked Example

Calculate the kinetic energy of a man of mass 80kg running at a speed of 7m/s.

KE = (mv2)÷2

KE = (80 x 72) ÷2

KE = 1960J

<h2 id="gravitational-potential-energy">Gravitational Potential Energy</h2>

Gravitational Potential energy is the energy stored by an object due to the gravitational field of the Earth (or other planet). As you lift an object higher above the Earth, it gains gravitational potential energy. If the object falls back down again, it loses gravitational potential energy.

Gravitational Potential Energy can be calculated using this equation: (you DO need to memorise this equation)

GPE = mgh

GPE = gravitational potential energy

m = mass (kg)

__g __= gravitational field strength (9.81 N/kg on the Earth)

h = height (m)

__OR __(because W=mg), this equation can be used:

GPE = Wh

W = weight (N)

Worked Example

Calculate the gravitational potential energy gained by a pupil of mass 50kg who walks up 3 flights of stairs to a height of 15m. (gravitational field strength = 9.81 N/kg)

GPE = mgh

GPE = 50 x 9.81 x 15

GPE = 7358J

<h2 id="dissipation-of-energy">Dissipation of Energy</h2>

<ol>
 <li>Friction is a force exerted on an object sliding across another object</li>
 <li>Friction transfers energy as heat</li>
 <li>Heat energy is transferred to the surroundings which become slightly warmer</li>
 <li>As energy dissipates (spreads out) it gets less and less useful</li>
 <li>This dissipated energy is commonly referred to as ‘wasted’ energy</li>
</ol>

Watch the following video to see an example of conservation and dissipation of energy in action:



In this video, the bowling ball does not hit the person’s face because:

<ol>
 <li>GPE is converted into KE as the ball travels downwards</li>
 <li>KE is converted back into GPE as the ball travels up the other side</li>
 <li>As the ball travels through the air it encounters air resistance</li>
 <li>This means some energy is __dissipated __as heat in the air</li>
 <li>As some of the energy has been dissipated, the ball will not have as much GPE at the end of its journey as it did at the start</li>
 <li>Therefore the ball will not travel as high as its starting point</li>
</ol>

<dl>
	<dt>What is the energy input for an acoustic guitar?</dt>
	<dd id="Dissipation-of-Energy0" class="js-click-to-reveal">kinetic</dd>
	<dt>What is the increase in Gravitational Potential Energy when an object of weight 120N is lifted to a height of 5m?</dt>
	<dd id="Dissipation-of-Energy1" class="js-click-to-reveal">600</dd>
	<dt>How much kinetic energy does a man of mass 75kg have if he is walking at a speed of 2m/s?</dt>
	<dd id="Dissipation-of-Energy2" class="js-click-to-reveal">150</dd>
	<dt>At the top of the track, a rollercoaster has 1500J of GPE. Ignoring friction, how much Kinetic Energy would the rollercoaster have at the bottom of the track?</dt>
	<dd id="Dissipation-of-Energy3" class="js-click-to-reveal">1500</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Energy Transfer</h1>
</header>

<main class="blog-post__content">
	<h2 id="energy-transfer">Energy Transfer</h2>

	Energy exists in different forms (stores) and is transferred from one store to another.

	Examples of energy stores:

	<ol>
		<li>Light</li>
		<li>Sound</li>
		<li>Heat</li>
		<li>Chemical</li>
		<li>Electrical</li>
		<li>Kinetic (movement)</li>
		<li>Gravitational Potential (Stored by objects at a height)</li>
		<li>Elastic Potential (Stored by elastic materials)</li>
	</ol>

	Energy Transfer

	Devices transfer energy from one store (form) into another.

	<a href="/img/notes/12/Capture.jpg" target="_blank"><img class="img-20" src="/img/notes/12/Capture.jpg" alt="Energy Transfer, figure 1" /></a><a href="/img/notes/12/Capture2.jpg" target="_blank"><img class="img-20" src="/img/notes/12/Capture2.jpg" alt="Energy Transfer, figure 2" /></a>

	<ol>
		<li>A light bulb converts electrical energy into light</li>
		<li>A loudspeaker converts electrical energy into sound</li>
	</ol>

	<h2 id="sankey-diagrams">Sankey Diagrams</h2>

	A Sankey diagram shows the energy transfers for a particular device.

	<ol>
		<li>The energy supplied is shown at the start of the arrow</li>
		<li>The useful energy is shown by the arrow pointing straight ahead</li>
		<li>'Wasted' energy is shown by the arrow curving away from the useful energy</li>
	</ol>

	The size of the arrows represents the amount of energy.

	<a href="/img/notes/12/3.jpg" target="_blank"><img class="img-40" src="/img/notes/12/3.jpg" alt="Energy Transfer, figure 1" /></a>

	Example Sankey Diagrams:

	<a href="/img/notes/12/4.jpg" target="_blank"><img class="img-40" src="/img/notes/12/4.jpg" alt="Energy Transfer, figure 2" /></a><a href="/img/notes/12/5.jpg" target="_blank"><img class="img-40" src="/img/notes/12/5.jpg" alt="Energy Transfer, figure 3" /></a><a href="/img/notes/12/6.jpg" target="_blank"><img class="img-40" src="/img/notes/12/6.jpg" alt="Energy Transfer, figure 4" /></a>

	<h2 id="elastic-potential-energy">Elastic Potential Energy</h2>

	Elastic Potential Energy (EPE) is stored in elastic materials when they are stretched or squashed. The EPE causes them to move back to their original shape when released.

	For example:

	<a href="/img/notes/12/Screen-Shot-2018-01-25-at-20.51.30.png" target="_blank"><img class="img-20" src="/img/notes/12/Screen-Shot-2018-01-25-at-20.51.30.png" alt="Energy Transfer, figure 1" /></a>

	<ol>
		<li>Energy is used to stretch a catapult</li>
		<li>EPE is stored in the catapult while it is stretched</li>
		<li>EPE released (transformed into Kinetic Energy) when the catapult is released, causing the object to move forward</li>
	</ol>

	Elastic Potential Energy can be calculated using the following equation (you do NOT need to memorize this equation)

	EPE = (ke2)÷2

	EPE = Elastic Potential Energy (J)

	k = spring constant (N/m)

	e = extension (m)

	Worked Example 1

	Calculate the EPE stored in a spring with spring constant 250N/m when it is stretched to extend by 0.2m

	EPE = ke2÷2

	EPE = 250 x 0.22÷2

	EPE = 5J

	Worked Example 2

	If a spring with spring constant 300N/m has 20J of EPE, how much has it extended?

	e = √(2EPE÷ k)

	e = √(2x20÷ 300)

	e = 0.37m

	<h2 id="kinetic-energy">Kinetic Energy</h2>

	Kinetic energy is the energy possessed by a moving object. It depends on the velocity (speed) of the object and the mass of the object.

	Kinetic Energy can be calculated using this equation: (you DO need to memorize this equation)

	KE = (mv2)÷2

	KE = Kinetic Energy (J)

	m = mass (kg)

	v = velocity (m/s)

	Rearranging this equation to find velocity can be a bit tricky!

	v = √(2KE ÷ m)

	Worked Example

	Calculate the kinetic energy of a man of mass 80kg running at a speed of 7m/s.

	KE = (mv2)÷2

	KE = (80 x 72) ÷2

	KE = 1960J

	<h2 id="gravitational-potential-energy">Gravitational Potential Energy</h2>

	Gravitational Potential energy is the energy stored by an object due to the gravitational field of the Earth (or other planet). As you lift an object higher above the Earth, it gains gravitational potential energy. If the object falls back down again, it loses gravitational potential energy.

	Gravitational Potential Energy can be calculated using this equation: (you DO need to memorize this equation)

	GPE = mgh

	GPE = gravitational potential energy

	m = mass (kg)

	g = gravitational field strength (9.81 N/kg on the Earth)

	h = height (m)

	OR (because W=mg), this equation can be used:

	GPE = Wh

	W = weight (N)

	Worked Example

	Calculate the gravitational potential energy gained by a pupil of mass 50kg who walks up 3 flights of stairs to a height of 15m. (gravitational field strength = 9.81 N/kg)

	GPE = mgh

	GPE = 50 x 9.81 x 15

	GPE = 7358J

	<h2 id="dissipation-of-energy">Dissipation of Energy</h2>

	<ol>
		<li>Friction is a force exerted on an object sliding across another object</li>
		<li>Friction transfers energy as heat</li>
		<li>Heat energy is transferred to the surroundings which become slightly warmer</li>
		<li>As energy dissipates (spreads out) it gets less and less useful</li>
		<li>This dissipated energy is commonly referred to as 'wasted' energy</li>
	</ol>

	Watch the following video to see an example of conservation and dissipation of energy in action:

	

	In this video, the bowling ball does not hit the person's face because:

	<ol>
		<li>GPE is converted into KE as the ball travels downwards</li>
		<li>KE is converted back into GPE as the ball travels up the other side</li>
		<li>As the ball travels through the air it encounters air resistance</li>
		<li>This means some energy is dissipated as heat in the air</li>
		<li>As some of the energy has been dissipated, the ball will not have as much GPE at the end of its journey as it did at the start</li>
		<li>Therefore the ball will not travel as high as its starting point</li>
	</ol>

	<dl>
		<dt>What is the energy input for an acoustic guitar?</dt>
		<dd id="Dissipation-of-Energy0" class="js-click-to-reveal">kinetic</dd>
		<dt>What is the increase in Gravitational Potential Energy when an object of weight 120N is lifted to a height of 5m?</dt>
		<dd id="Dissipation-of-Energy1" class="js-click-to-reveal">600</dd>
		<dt>How much kinetic energy does a man of mass 75kg have if he is walking at a speed of 2m/s?</dt>
		<dd id="Dissipation-of-Energy2" class="js-click-to-reveal">150</dd>
		<dt>At the top of the track, a rollercoaster has 1500J of GPE. Ignoring friction, how much Kinetic Energy would the rollercoaster have at the bottom of the track?</dt>
		<dd id="Dissipation-of-Energy3" class="js-click-to-reveal">1500</dd>
	</dl>


</main>

Energy Transfer

<header>
			<h1 class="blog-post__title">Static Electricity</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="static-electricity">Static Electricity</h2>

An atom consists of a nucleus (containing positively charged protons and neutral neutrons) orbited by negatively charged electrons.

<img src="/img/notes/02/1.png" alt="Static Electricity, figure 1" /></a>

Electricity is the movement of these electrons.

Charged objects can experience a non-contact force because they are surrounded by an electric field. The field lines point away from a positive source and towards a negative source.

<img src="/img/notes/02/2.png" alt="Static Electricity, figure 2" /></a>

A second charged object entering that field will experience a force.

Like charges repel.

Unlike charges attract.

<img src="/img/notes/02/3.png" alt="Static Electricity, figure 3" /></a>

Friction can cause electrons to move from one object to another. If the objects are conductors, the electrons will just flow back to where they came from, but if the objects are insulators, the electrons can not flow back. In this case the objects have become charged.

<ol>
 <li>The object that gains electrons becomes negatively charged</li>
 <li>The object that loses electrons becomes positively charged</li>
</ol>

<h2 id="induced-charge">Induced Charge</h2>

If a charged object is brought near to a neutral object, it can induce a charge. Electrons are repelled from a negative object, protons are attracted. If the object has a low mass, the force of attraction/repulsion may move the object.

<img src="/img/notes/02/ezgif.com-resize.gif" alt="Static Electricity, figure 1" /></a>

<h2 id="van-der-graaff-generator">Van der Graaff Generator</h2>

The Van der Graaff generator is a classic demonstration of static electricity. A belt rubs on the inside of a metal sphere and the friction causes electrons to move onto the sphere. The sphere is supported by a plastic (insulating) stand and so the electrons build up on the sphere.

<img src="/img/notes/02/vdg.jpg" alt="Static Electricity, figure 1" /></a>

This means that the sphere builds up a negative charge. This charge will remain on the sphere until a conducting object comes close enough to allow the electrons to discharge (flow to the earth). If you reached out to touch the sphere while it was charged, the electrons would discharge through you and you would experience an electric shock.

If you are touching the sphere (as it is turned on), you also build up the charge.

Negatively charged objects will repel each other and so each negatively-charged hair on your head will repel the negatively-charged hair next to it. As a result, your hair stands on end!

<img src="/img/notes/02/vdg2.jpg" alt="Static Electricity, figure 2" /></a>

<dl>
	<dt>What causes electrons to move from one object to another?</dt>
	<dd id="Van-der-Graaff-Generator0" class="js-click-to-reveal">friction</dd>
	<dt>What charge will an object have if it gains electrons?</dt>
	<dd id="Van-der-Graaff-Generator1" class="js-click-to-reveal">negative</dd>
	<dt>Two negatively charged objects will ______. </dt>
	<dd id="Van-der-Graaff-Generator2" class="js-click-to-reveal">repel</dd>
	<dt>A negatively charged object and a positively charged object will ________. </dt>
	<dd id="Van-der-Graaff-Generator3" class="js-click-to-reveal">attract</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Static Electricity</h1>
</header>

<main class="blog-post__content">
	<h2 id="static-electricity">Static Electricity</h2>

	An atom consists of a nucleus (containing positively charged protons and neutral neutrons) orbited by negatively charged electrons.

	<a href="/img/notes/02/1.png" target="_blank"><img src="/img/notes/02/1.png" alt="Static Electricity, figure 1" /></a>

	Electricity is the movement of these electrons.

	Charged objects can experience a non-contact force because they are surrounded by an electric field. The field lines point away from a positive source and towards a negative source.

	<a href="/img/notes/02/2.png" target="_blank"><img src="/img/notes/02/2.png" alt="Static Electricity, figure 2" /></a>

	A second charged object entering that field will experience a force.

	Like charges repel, and unlike charges attract.

	<a href="/img/notes/02/3.png" target="_blank"><img src="/img/notes/02/3.png" alt="Static Electricity, figure 3" /></a>

	Friction can cause electrons to move from one object to another. If the objects are conductors, the electrons will just flow back to where they came from, but if the objects are insulators, the electrons cannot flow back. In this case, the objects have become charged.

	<ol>
		<li>The object that gains electrons becomes negatively charged.</li>
		<li>The object that loses electrons becomes positively charged.</li>
	</ol>

	<h2 id="induced-charge">Induced Charge</h2>

	If a charged object is brought near to a neutral object, it can induce a charge. Electrons are repelled from a negative object, and protons are attracted. If the object has a low mass, the force of attraction/repulsion may move the object.

	<a href="/img/notes/02/ezgif.com-resize.gif" target="_blank"><img src="/img/notes/02/ezgif.com-resize.gif" alt="Static Electricity, figure 1" /></a>

	<h2 id="van-der-graaff-generator">Van der Graaff Generator</h2>

	The Van der Graaff generator is a classic demonstration of static electricity. A belt rubs on the inside of a metal sphere, and the friction causes electrons to move onto the sphere. The sphere is supported by a plastic (insulating) stand, and so the electrons build up on the sphere.

	<a href="/img/notes/02/vdg.jpg" target="_blank"><img src="/img/notes/02/vdg.jpg" alt="Static Electricity, figure 1" /></a>

	This means that the sphere builds up a negative charge. This charge will remain on the sphere until a conducting object comes close enough to allow the electrons to discharge (flow to the earth). If you reach out to touch the sphere while it is charged, the electrons will discharge through you, and you will experience an electric shock.

	If you are touching the sphere (as it is turned on), you also build up the charge.

	Negatively charged objects will repel each other, and so each negatively charged hair on your head will repel the negatively charged hair next to it. As a result, your hair stands on end!

	<a href="/img/notes/02/vdg2.jpg" target="_blank"><img src="/img/notes/02/vdg2.jpg" alt="Static Electricity, figure 2" /></a>

	<dl>
		<dt>What causes electrons to move from one object to another?</dt>
		<dd id="Van-der-Graaff-Generator0" class="js-click-to-reveal">Friction</dd>
		<dt>What charge will an object have if it gains electrons?</dt>
		<dd id="Van-der-Graaff-Generator1" class="js-click-to-reveal">Negative</dd>
		<dt>Two negatively charged objects will ______. </dt>
		<dd id="Van-der-Graaff-Generator2" class="js-click-to-reveal">Repel</dd>
		<dt>A negatively charged object and a positively charged object will ________. </dt>
		<dd id="Van-der-Graaff-Generator3" class="js-click-to-reveal">Attract</dd>
	</dl>
</main>

Static Electricity

Electricity

<header>
			<h1 class="blog-post__title">Using Electricity</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="electrical-energy">Electrical Energy</h2>

The amount of electrical energy transferred to a device depends on:

<ol>
 <li>The time it is used for</li>
 <li>The power of the device (the rate at which it transfers energy)</li>
</ol>

Power is the rate of using energy. A 100W light bulb will use more electrical energy than a 60W bulb if they are both on for the same length of time

You need to remember the equation for power for your exam

<h3 class="ql-align-center">P = E ÷ t</h3>

P = power (W)

E = work done or energy transferred (J)

__t __= time (s)

<img src="/img/notes/01/a.png" alt="Using Electricity, figure 1" /></a>

<h2 id="worked-examples">Worked Examples</h2>

Worked Example 1

Calculate the electrical energy used by the following devices:

An iPhone used for 3 hours (Power = 2W)

3 hours = 10800s

E = Pt = 2 x 10800 = 21,600J

A hairdryer used for 10 minutes (Power = 1500W)

10 mins = 600s

E = Pt = 1500 x 600 = 900,000J

A laptop used for 5 hours (Power = 50W)

5 hours = 18000s

E = Pt = 50 x 18000 = 900,000J

There are also two other equations for power that you need to memorise:

Power = Current x Voltage

P = I V

<img src="/img/notes/01/b.png" alt="Using Electricity, figure 1" /></a>

Also, because Potential Difference = current x resistance…

Power = Current2__ x Resistance__

P = I2__ R__

<img src="/img/notes/02/4.png" alt="Using Electricity, figure 2" /></a>

Worked Example 2

What is the power of a 12V lamp with a current of 2A flowing through it?

Power = current x voltage

Power = 2 x 12

Power = 24W

Worked Example 3

A hairdryer has a resistance of 120Ω and draws a current of 4A. What is it’s power?

Power = current2 x resistance

Power = 42 x 120

Power = 1920W

<h2 id="fuses">Fuses</h2>

A fuse protects an electrical device.

It contains a thin piece of wire which will melt and break the circuit if the current is too high.

This prevents damage to the device.

The rating of the fuse is the maximum current that the fuse can conduct.

<img src="/img/notes/02/5.png" alt="Using Electricity, figure 1" /></a>

Fuses are labelled with the maximum current they are designed to allow.

When choosing the fuse for a device you should always choose one with the ampage above the operating current of the device.

For example, if a kettle operates with an electrical current of 4.3A and the available fuses are 3A, 5A, and 13A, then you should choose the 5A fuse.

<h2 id="uk-mains-electricity">UK Mains Electricity</h2>

<ol>
 <li>AC supply</li>
 <li>Frequency = 50 Hz (changes direction 50 times per second)</li>
 <li>Potential Difference = 230V</li>
</ol>

<h2 id="generating-electricity">Generating Electricity</h2>

Electricity in generated in power stations using Electromagnetic Induction - When a magnet is moved in a coil of wire, current is induced in the coil.

<img src="/img/notes/02/giphy-downsized.gif" alt="Using Electricity, figure 1" /></a>

Alternating Current (AC) is produced – this means the direction of the current changes direction repeatedly. In the UK, the mains electrical supply has a frequency of 50Hz – it changes direction 50 times per second.

<img src="/img/notes/02/6.png" alt="Using Electricity, figure 2" /></a>

<ol>
 <li>Amplitude = peak voltage of the supply</li>
 <li>Period = time for one complete wave</li>
 <li>Frequency = number of waves per second</li>
 <li>Frequency = 1 ÷ period</li>
</ol>

The size of the induced current can be increased by:

<ol>
 <li>Increasing the strength of the magnet</li>
 <li>Increasing the number of turns of wire on the coil</li>
 <li>Placing an iron core inside the coil</li>
 <li>Increasing the speed of the rotation</li>
</ol>

<img src="/img/notes/02/7.png" alt="Using Electricity, figure 3" /></a><img src="/img/notes/02/8.png" alt="Using Electricity, figure 4" /></a>

<h2 id="cables-and-plugs">Cables and Plugs</h2>

In the UK, most devices use a 3-core cable (the electrical cable has three separate wires inside)

<img src="/img/notes/02/9.png" alt="Using Electricity, figure 1" /></a>

Brown – live

Blue – neutral

Green/Yellow – earth

These are connected to 3 pin plugs:

<img src="/img/notes/02/10.png" alt="Using Electricity, figure 2" /></a><img src="/img/notes/02/11.png" alt="Using Electricity, figure 3" /></a>

The Earth pin is at the top with the live and neutral pins at the bottom. The fuse connected to live wire. There is a cable grip to keep the wires in place.

What does each wire do?

<ol>
 <li>The live wire constantly alternates between a positive and negative voltage</li>
 <li>The neutral wire is at 0V</li>
 <li>The potential difference (or voltage) supplied to the device is the difference between the live and neutral wires</li>
 <li>The earth wire is connected to any external metal parts of the device. If the live wire breaks and touches the case, the electric current would flow away through the earth wire, preventing the outside of the device becoming live</li>
</ol>

Double Insulation

<ol>
 <li>Devices with no external metal parts do not need an earth wire</li>
 <li>These devices are known as ‘double insulated’</li>
 <li>The earth pin will often be made of plastic for double insulated devices</li>
</ol>

<img src="/img/notes/02/13.png" alt="Using Electricity, figure 4" /></a><img src="/img/notes/02/12.png" alt="Using Electricity, figure 5" /></a>

<h2 id="national-grid">National Grid</h2>

The National Grid is a network of wires and pylons connecting power stations and consumers together

<img src="/img/notes/02/grid-1024x682.jpg" alt="Using Electricity, figure 1" /></a>

Transformers

A transformer is a device which is used to increase or decrease voltage (potential difference)

<img src="/img/notes/02/14.png" alt="Using Electricity, figure 2" /></a>

<ol>
 <li>A STEP UP transformer increases the voltage. It has more turns on the secondary coil.</li>
 <li>A STEP DOWN transformer decreases the voltage. It has less turns on the secondary coil.</li>
</ol>

Every power station feeds into the grid and every consumer takes electricity from the grid. Transformers are used to step up voltage from power station to the grid and to step down voltage from the grid to homes (230V).

<img src="/img/notes/02/grid-2.png" alt="Using Electricity, figure 3" /></a>

High voltages are used between pylons (400,000 V) so that less energy is lost (high voltage = low current at constant power [P=IV])

<dl>
	<dt>What colour is the neutral wire?</dt>
	<dd id="National-Grid0" class="js-click-to-reveal">blue</dd>
	<dt>Which wire is attached to the fuse in a plug?</dt>
	<dd id="National-Grid1" class="js-click-to-reveal">live</dd>
	<dt>A 1.5W heater is used with the (230V) mains supply, how much current does it take?</dt>
	<dd id="National-Grid2" class="js-click-to-reveal">Your answer should include: 6.5A / 6.5</dd>
	<dt>A cable can take a maximum current of 2A when connected to the mains voltage. What is the maximum power that can be carried by this cable?</dt>
	<dd id="National-Grid3" class="js-click-to-reveal">460W. 460</dd>
	<dt>What is the frequency of the UK AC supply?</dt>
	<dd id="National-Grid4" class="js-click-to-reveal">Your answer should include: 50Hz / 50</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Using Electricity</h1>
</header>

<main class="blog-post__content">
	<h2 id="electrical-energy">Electrical Energy</h2>

	The amount of electrical energy transferred to a device depends on:

	<ol>
		<li>The time it is used for</li>
		<li>The power of the device (the rate at which it transfers energy)</li>
	</ol>

	Power is the rate of using energy. A 100W light bulb will use more electrical energy than a 60W bulb if they are both on for the same length of time.

	Remember the equation for power for your exam:

	<h3 class="ql-align-center">P = E ÷ t</h3>

	P = power (W)

	E = work done or energy transferred (J)

	t = time (s)

	<img class="img-20" src="/img/notes/01/a.png" alt="Using Electricity, figure 1" />

	<h2 id="worked-examples">Worked Examples</h2>

	Worked Example 1

	Calculate the electrical energy used by the following devices:

	An iPhone used for 3 hours (Power = 2W)

	3 hours = 10800s

	E = Pt = 2 x 10800 = 21,600J

	A hairdryer used for 10 minutes (Power = 1500W)

	10 mins = 600s

	E = Pt = 1500 x 600 = 900,000J

	A laptop used for 5 hours (Power = 50W)

	5 hours = 18000s

	E = Pt = 50 x 18000 = 900,000J

	There are also two other equations for power that you need to memorize:

	Power = Current x Voltage

	P = IV

	<img class="img-20" src="/img/notes/01/b.png" alt="Using Electricity, figure 1" />

	Also, because Potential Difference = current x resistance…

	Power = Current2 x Resistance

	P = I2R

	<img class="img-20" src="/img/notes/02/4.png" alt="Using Electricity, figure 2" />

	Worked Example 2

	What is the power of a 12V lamp with a current of 2A flowing through it?

	Power = current x voltage

	Power = 2 x 12

	Power = 24W

	Worked Example 3

	A hairdryer has a resistance of 120Ω and draws a current of 4A. What is its power?

	Power = current2 x resistance

	Power = 42 x 120

	Power = 1920W

	<h2 id="fuses">Fuses</h2>

	A fuse protects an electrical device.

	It contains a thin piece of wire which will melt and break the circuit if the current is too high.

	This prevents damage to the device.

	The rating of the fuse is the maximum current that the fuse can conduct.

	<img src="/img/notes/02/5.png" alt="Using Electricity, figure 1" />

	Fuses are labeled with the maximum current they are designed to allow.

	When choosing the fuse for a device, you should always choose one with the amperage above the operating current of the device.

	For example, if a kettle operates with an electrical current of 4.3A and the available fuses are 3A, 5A, and 13A, then you should choose the 5A fuse.

	<h2 id="uk-mains-electricity">UK Mains Electricity</h2>

	<ol>
		<li>AC supply</li>
		<li>Frequency = 50 Hz (changes direction 50 times per second)</li>
		<li>Potential Difference = 230V</li>
	</ol>

	<h2 id="generating-electricity">Generating Electricity</h2>

	Electricity is generated in power stations using Electromagnetic Induction - When a magnet is moved in a coil of wire, current is induced in the coil.

	<img src="/img/notes/02/giphy-downsized.gif" alt="Using Electricity, figure 1" />

	Alternating Current (AC) is produced – this means the direction of the current changes direction repeatedly. In the UK, the mains electrical supply has a frequency of 50Hz – it changes direction 50 times per second.

	<img src="/img/notes/02/6.png" alt="Using Electricity, figure 2" />

	<ol>
		<li>Amplitude = peak voltage of the supply</li>
		<li>Period = time for one complete wave</li>
		<li>Frequency = number of waves per second</li>
		<li>Frequency = 1 ÷ period</li>
	</ol>

	The size of the induced current can be increased by:

	<ol>
		<li>Increasing the strength of the magnet</li>
		<li>Increasing the number of turns of wire on the coil</li>
		<li>Placing an iron core inside the coil</li>
		<li>Increasing the speed of the rotation</li>
	</ol>

	<img src="/img/notes/02/7.png" alt="Using Electricity, figure 3" /><img src="/img/notes/02/8.png" alt="Using Electricity, figure 4" />

	<h2 id="cables-and-plugs">Cables and Plugs</h2>

	In the UK, most devices use a 3-core cable (the electrical cable has three separate wires inside)

	<img src="/img/notes/02/9.png" alt="Using Electricity, figure 1" />

	Brown – live

	Blue – neutral

	Green/Yellow – earth

	These are connected to 3 pin plugs:

	<img class="img-30" src="/img/notes/02/10.png" alt="Using Electricity, figure 2" /><img class="img-40" src="/img/notes/02/11.png" alt="Using Electricity, figure 3" />

	The Earth pin is at the top with the live and neutral pins at the bottom. The fuse is connected to the live wire. There is a cable grip to keep the wires in place.

	What does each wire do?

	<ol>
		<li>The live wire constantly alternates between a positive and negative voltage</li>
		<li>The neutral wire is at 0V</li>
		<li>The potential difference (or voltage) supplied to the device is the difference between the live and neutral wires</li>
		<li>The earth wire is connected to any external metal parts of the device. If the live wire breaks and touches the case, the electric current would flow away through the earth wire, preventing the outside of the device from becoming live</li>
	</ol>

	Double Insulation

	<ol>
		<li>Devices with no external metal parts do not need an earth wire</li>
		<li>These devices are known as ‘double insulated’</li>
		<li>The earth pin will often be made of plastic for double insulated devices</li>
	</ol>

	<img class="img-20" src="/img/notes/02/13.png" alt="Using Electricity, figure 4" /><img class="img-30" src="/img/notes/02/12.png" alt="Using Electricity, figure 5" />

	<h2 id="national-grid">National Grid</h2>

	The National Grid is a network of wires and pylons connecting power stations and consumers together

	<img src="/img/notes/02/grid-1024x682.jpg" alt="Using Electricity, figure 1" />

	Transformers

	A transformer is a device which is used to increase or decrease voltage (potential difference)

	<img src="/img/notes/02/14.png" alt="Using Electricity, figure 2" />

	<ol>
		<li>A STEP UP transformer increases the voltage. It has more turns on the secondary coil.</li>
		<li>A STEP DOWN transformer decreases the voltage. It has fewer turns on the secondary coil.</li>
	</ol>

	Every power station feeds into the grid and every consumer takes electricity from the grid. Transformers are used to step up voltage from power station to the grid and to step down voltage from the grid to homes (230V).

	<img src="/img/notes/02/grid-2.png" alt="Using Electricity, figure 3" />

	High voltages are used between pylons (400,000 V) so that less energy is lost (high voltage = low current at constant power [P=IV])

	<dl>
		<dt>What colour is the neutral wire?</dt>
		<dd id="National-Grid0" class="js-click-to-reveal">blue</dd>
		<dt>Which wire is attached to the fuse in a plug?</dt>
		<dd id="National-Grid1" class="js-click-to-reveal">live</dd>
		<dt>A 1.5W heater is used with the (230V) mains supply, how much current does it take?</dt>
		<dd id="National-Grid2" class="js-click-to-reveal">Your answer should include: 6.5A / 6.5</dd>
		<dt>A cable can take a maximum current of 2A when connected to the mains voltage. What is the maximum power that can be carried by this cable?</dt>
		<dd id="National-Grid3" class="js-click-to-reveal">460W. 460</dd>
		<dt>What is the frequency of the UK AC supply?</dt>
		<dd id="National-Grid4" class="js-click-to-reveal">Your answer should include: 50Hz / 50</dd>
	</dl>
</main>

Using Electricity

<header>
			<h1 class="blog-post__title">Resistance</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="resistance">Resistance</h2>

Resistance is opposition to the flow of current. A high resistance means it is harder for current to flow through. A low resistance means current will flow through more easily.

Resistance is measured in Ohms (Ω).

<img src="/img/notes/02/10.jpg" alt="Resistance, figure 1" /></a>

<h2 id="ohms-law">Ohm’s Law</h2>

Ohm’s law states that current is directly proportional to potential difference (providing the temperature remains constant).

It can be summarised in the equation (you DO need to remember this equation for your exam):

Voltage = Current x Resistance

V = I x R

V = Voltage (Volts)

__I __= Current (Amps)

R = Resistance (Ω)

<h2 id="measuring-resistance">Measuring Resistance</h2>

To measure the resistance of a component, a standard test circuit is used to measure the current flowing through the component and the potential difference across it. The equation above can then be used to calculate resistance

<img src="/img/notes/02/11.jpg" alt="Resistance, figure 1" /></a>

<h2 id="required-practical--resistance-of-a-wire">Required Practical – Resistance of a Wire</h2>

You need to be familiar with the practical procedure used to investigate the factors affecting the resistance of a wire.

The factors affecting the resistance of a wire are:

<ol>
 <li>Length</li>
 <li>Cross-sectional area (thickness)</li>
 <li>Material</li>
 <li>Temperature</li>
</ol>

They can be investigated using a standard test circuit:

<img src="/img/notes/02/12.jpg" alt="Resistance, figure 1" /></a>

If investigating length:

<ol>
 <li>Measure and record the current and potential difference across the wire</li>
 <li>Calculate resistance using V=IR</li>
 <li>Repeat for different lengths of wire (keeping the material, thickness and temperature constant)</li>
</ol>

The same method can be used to investigate the other variables.

When the results are analysed, the following patterns should be observed:

<ol>
 <li>Length - The longer the wire the higher the resistance. This should be a directly proportional relationship. As the wire length is increased, the same potential difference is driving current through a longer length and so less electrons will flow.</li>
 <li>Cross -sectional area – The thinner the wire, the greater the resistance. A thinner wire has less electrons available to move, so less current will flow when the same potential difference is applied.</li>
 <li>Temperature – The higher the temperature of the wire, the greater the resistance. As temperature increases, the atoms in the wire have more kinetic energy and vibrate faster, making it harder for electrons to pass through</li>
 <li>Material – Different materials have different resistivity. This is not a continuous variable and so, unlike the previous three, could only be plotted on a bar chart.</li>
</ol>

Possible causes of error in this investigation include:

<ol>
 <li>Inaccurate measurement of wire – the crocodile clips used to connect the wire in the circuit are a few mm wide and this could lead to the length of wire conducting electricity being slightly shorter than intended. This could be improved by using thinner contacts.</li>
 <li>Temperature – it is difficult to control the temperature of the wire and, as the investigation takes place, it is likely to heat up, which affects the resistance of the wire. This could be improved by letting the wire cool down to room temperature in between each measurement.</li>
</ol>

<h2 id="resistors-in-series-and-parallel">Resistors in Series and Parallel</h2>

Resistors in Series

The total resistance increases as more resistors are added in series​. The same voltage is being used to push current through a harder circuit, therefore less current travels​.

The resistance can be calculated using the equation (you do NOT need to remember this equation):

<img src="/img/notes/02/13.jpg" alt="Resistance, figure 1" /></a>

<img src="/img/notes/02/14.jpg" alt="Resistance, figure 2" /></a>

Resistors in Parallel﻿

The total resistance decreases as more resistors are added in series​. Each branch of a parallel circuit receives the same voltage and so, overall, more current is pushed around the circuit.

The resistance can be calculated using the equation (you do NOT need to remember this equation):

<img src="/img/notes/02/15.jpg" alt="Resistance, figure 3" /></a>

<img src="/img/notes/02/16.jpg" alt="Resistance, figure 4" /></a>

<h2 id="iv-graphs">IV Graphs</h2>

A current-voltage (or IV) graph shows how resistance varies for a component​. The negative section of the graph shows what happens if the direction of the current is reversed.

<img src="/img/notes/02/17.jpg" alt="Resistance, figure 1" /></a>

A fixed resistor obeys Ohm’s law and produces a directly proportional​ IV graph. The graph is symmetrical as the same relationship exists when current flows in the opposite direction through the resistor.

<img src="/img/notes/02/17.jpg" alt="Resistance, figure 2" /></a>

A filament bulb gets hot as current flows through it. This causes the resistance to increase and the IV graph to curve. The graph is symmetrical as the same relationship exists when current flows in the opposite direction through the bulb.

<img src="/img/notes/02/18.jpg" alt="Resistance, figure 3" /></a>

A diode only lets current flow in one direction. The IV graph has no current flowing in the reverse direction.

<img src="/img/notes/02/19.jpg" alt="Resistance, figure 4" /></a>

<h2 id="components">Components</h2>

You need to be familiar with the following components – their circuit symbol and their function.

<ol>
 <li>LDR - Light Dependant Resistor​. Resistance decreases when light intensity increases</li>
</ol>

<img src="/img/notes/02/20.jpg" alt="Resistance, figure 1" /></a>

<ol>
 <li>Thermistor - Resistance decreases as the temperature increases​</li>
</ol>

<img src="/img/notes/02/21.jpg" alt="Resistance, figure 2" /></a>

<ol>
 <li>LED - Light Emitting Diode​. Glows when current flows through it in the forward direction​</li>
</ol>

<img src="/img/notes/02/22.jpg" alt="Resistance, figure 3" /></a>

<dl>
	<dt>What is the resistance of the heating element in an electric kettle that uses mains voltage (230V) and a current of 10A?</dt>
	<dd id="Components0" class="js-click-to-reveal">23</dd>
	<dt>A 12V filament light bulb has a resistance of 60Ω. What current flows through the bulb?</dt>
	<dd id="Components1" class="js-click-to-reveal">2</dd>
	<dt>A hairdryer using mains voltage (230V) has a current of 5A flowing through the motor. What is the resistance of the motor?</dt>
	<dd id="Components2" class="js-click-to-reveal">46</dd>
	<dt>A remote controlled car uses three 1.5V batteries. If its resistance is 15Ω, what current flows through it?</dt>
	<dd id="Components3" class="js-click-to-reveal">3</dd>
	<dt>A 6V battery is used to power a portable speaker that has a resistance of 4Ω. What current flows through the speaker?</dt>
	<dd id="Components4" class="js-click-to-reveal">1.5</dd>
</dl>


		</main>

<header>
			<h1 class="blog-post__title">Resistance</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="resistance">Resistance</h2>

Resistance is the opposition to the flow of current. A high resistance means it is harder for current to flow through. A low resistance means current will flow more easily.

Resistance is measured in Ohms (Ω).

<a href="/img/notes/02/10.jpg" target="_blank"><img class="img-30" src="/img/notes/02/10.jpg" alt="Resistance, figure 1" /></a>

<h2 id="ohms-law">Ohm’s Law</h2>

Ohm’s law states that current is directly proportional to potential difference (providing the temperature remains constant).

It can be summarized in the equation (you DO need to remember this equation for your exam):

Voltage = Current x Resistance

V = I x R

V = Voltage (Volts)

I = Current (Amps)

R = Resistance (Ω)

<h2 id="measuring-resistance">Measuring Resistance</h2>

To measure the resistance of a component, a standard test circuit is used to measure the current flowing through the component and the potential difference across it. The equation above can then be used to calculate resistance.

<a href="/img/notes/02/11.jpg" target="_blank"><img class="img-30" src="/img/notes/02/11.jpg" alt="Resistance, figure 1" /></a>

<h2 id="required-practical--resistance-of-a-wire">Required Practical – Resistance of a Wire</h2>

You need to be familiar with the practical procedure used to investigate the factors affecting the resistance of a wire.

The factors affecting the resistance of a wire are:

<ol>
 <li>Length</li>
 <li>Cross-sectional area (thickness)</li>
 <li>Material</li>
 <li>Temperature</li>
</ol>

They can be investigated using a standard test circuit:

<a href="/img/notes/02/12.jpg" target="_blank"><img class="img-30" src="/img/notes/02/12.jpg" alt="Resistance, figure 1" /></a>

If investigating length:

<ol>
 <li>Measure and record the current and potential difference across the wire</li>
 <li>Calculate resistance using V=IR</li>
 <li>Repeat for different lengths of wire (keeping the material, thickness, and temperature constant)</li>
</ol>

The same method can be used to investigate the other variables.

When the results are analyzed, the following patterns should be observed:

<ol>
 <li>Length - The longer the wire, the higher the resistance. This should be a directly proportional relationship. As the wire length is increased, the same potential difference is driving current through a longer length, and so fewer electrons will flow.</li>
 <li>Cross-sectional area – The thinner the wire, the greater the resistance. A thinner wire has fewer electrons available to move, so less current will flow when the same potential difference is applied.</li>
 <li>Temperature – The higher the temperature of the wire, the greater the resistance. As temperature increases, the atoms in the wire have more kinetic energy and vibrate faster, making it harder for electrons to pass through.</li>
 <li>Material – Different materials have different resistivity. This is not a continuous variable and so, unlike the previous three, could only be plotted on a bar chart.</li>
</ol>

Possible causes of error in this investigation include:

<ol>
 <li>Inaccurate measurement of wire – the crocodile clips used to connect the wire in the circuit are a few mm wide and this could lead to the length of wire conducting electricity being slightly shorter than intended. This could be improved by using thinner contacts.</li>
 <li>Temperature – it is difficult to control the temperature of the wire and, as the investigation takes place, it is likely to heat up, which affects the resistance of the wire. This could be improved by letting the wire cool down to room temperature in between each measurement.</li>
</ol>

<h2 id="resistors-in-series-and-parallel">Resistors in Series and Parallel</h2>

Resistors in Series

The total resistance increases as more resistors are added in series. The same voltage is being used to push current through a harder circuit, therefore less current travels.

The resistance can be calculated using the equation (you do NOT need to remember this equation):

<a href="/img/notes/02/13.jpg" target="_blank"><img class="img-30" src="/img/notes/02/13.jpg" alt="Resistance, figure 1" /></a>

<a href="/img/notes/02/14.jpg" target="_blank"><img class="img-30" src="/img/notes/02/14.jpg" alt="Resistance, figure 2" /></a>

Resistors in Parallel

The total resistance decreases as more resistors are added in parallel. Each branch of a parallel circuit receives the same voltage and so, overall, more current is pushed around the circuit.

The resistance can be calculated using the equation (you do NOT need to remember this equation):

<a href="/img/notes/02/15.jpg" target="_blank"><img class="img-30" src="/img/notes/02/15.jpg" alt="Resistance, figure 3" /></a>

<a href="/img/notes/02/16.jpg" target="_blank"><img class="img-30" src="/img/notes/02/16.jpg" alt="Resistance, figure 4" /></a>

<h2 id="iv-graphs">IV Graphs</h2>

A current-voltage (or IV) graph shows how resistance varies for a component. The negative section of the graph shows what happens if the direction of the current is reversed.

<a href="/img/notes/02/17.jpg" target="_blank"><img class="img-30" src="/img/notes/02/17.jpg" alt="Resistance, figure 1" /></a>

A fixed resistor obeys Ohm’s law and produces a directly proportional IV graph. The graph is symmetrical as the same relationship exists when current flows in the opposite direction through the resistor.

<a href="/img/notes/02/17.jpg" target="_blank"><img class="img-30" src="/img/notes/02/17.jpg" alt="Resistance, figure 2" /></a>

A filament bulb gets hot as current flows through it. This causes the resistance to increase and the IV graph to curve. The graph is symmetrical as the same relationship exists when current flows in the opposite direction through the bulb.

<a href="/img/notes/02/18.jpg" target="_blank"><img class="img-30" src="/img/notes/02/18.jpg" alt="Resistance, figure 3" /></a>

A diode only lets current flow in one direction. The IV graph has no current flowing in the reverse direction.

<a href="/img/notes/02/19.jpg" target="_blank"><img class="img-30" src="/img/notes/02/19.jpg" alt="Resistance, figure 4" /></a>

<h2 id="components">Components</h2>

You need to be familiar with the following components – their circuit symbol and their function.

<ol>
 <li>LDR - Light Dependent Resistor. Resistance decreases when light intensity increases</li>
</ol>

<a href="/img/notes/02/20.jpg" target="_blank"><img class="img-30" src="/img/notes/02/20.jpg" alt="Resistance, figure 1" /></a>

<ol>
 <li>Thermistor - Resistance decreases as the temperature increases</li>
</ol>

<a href="/img/notes/02/21.jpg" target="_blank"><img class="img-30" src="/img/notes/02/21.jpg" alt="Resistance, figure 2" /></a>

<ol>
 <li>LED - Light Emitting Diode. Glows when current flows through it in the forward direction</li>
</ol>

<a href="/img/notes/02/22.jpg" target="_blank"><img class="img-30" src="/img/notes/02/22.jpg" alt="Resistance, figure 3" /></a>

<dl>
	<dt>What is the resistance of the heating element in an electric kettle that uses mains voltage (230V) and a current of 10A?</dt>
	<dd id="Components0" class="js-click-to-reveal">23</dd>
	<dt>A 12V filament light bulb has a resistance of 60Ω. What current flows through the bulb?</dt>
	<dd id="Components1" class="js-click-to-reveal">2</dd>
	<dt>A hairdryer using mains voltage (230V) has a current of 5A flowing through the motor. What is the resistance of the motor?</dt>
	<dd id="Components2" class="js-click-to-reveal">46</dd>
	<dt>A remote-controlled car uses three 1.5V batteries. If its resistance is 15Ω, what current flows through it?</dt>
	<dd id="Components3" class="js-click-to-reveal">3</dd>
	<dt>A 6V battery is used to power a portable speaker that has a resistance of 4Ω. What current flows through the speaker?</dt>
	<dd id="Components4" class="js-click-to-reveal">1.5</dd>
</dl>


		</main>

Resistance

<header>
			<h1 class="blog-post__title">Circuits</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="circuit-symbols">Circuit Symbols</h2>

All circuit diagrams use a set of established symbols. You need to be familiar with the circuit symbols below to understand the circuit diagrams that you may encounter in your exam.

<img src="/img/notes/02/1.jpg" alt="Circuits, figure 1" /></a>

<h2 id="series-and-parallel">Series and Parallel</h2>

Circuits can be categorised as series or parallel.

Series Circuits

<img src="/img/notes/02/2.jpg" alt="Circuits, figure 1" /></a>

In a series circuit:

<ol>
 <li>There is only one path around the circuit</li>
 <li>If one component breaks, all the other components will stop working</li>
 <li>More bulbs in series will cause the brightness of all the bulbs to decrease</li>
 <li>Switches will control all the bulbs together</li>
</ol>

Parallel Circuits

<img src="/img/notes/02/3.jpg" alt="Circuits, figure 2" /></a>

In a parallel circuit:

<ol>
 <li>There is more than one path around the circuit</li>
 <li>If one component breaks, the others stay on</li>
 <li>More bulbs added in parallel will be the same brightness as the original bulb</li>
 <li>Switches (on branches) will control bulbs individually</li>
</ol>

<h2 id="current">Current</h2>

Current is the flow of electrons (charged particles) around a circuit. Electrons are repelled from the negative end of the cell and attracted to the positive end.

Current is measured using an ammeter which is connected in series with the circuit.

<img src="/img/notes/02/4.jpg" alt="Circuits, figure 1" /></a>

The flow of charge can be calculated using this equation (you DO need to remember this for your exam):

<h3 class="ql-align-center">Q = It</h3>

Q = flow of charge (Coulombs, C)

I = current (Amps, A)

t = time (s)

Worked Example

A charge of 16C passes through a bulb in 5s. Calculate the current through the bulb

Q = It

I = Q ÷ t

I = 16 ÷5

I = 3.2A

Series

In a SERIES circuit, the current is always the same, no matter where you place the ammeter.

<img src="/img/notes/02/5.jpg" alt="Circuits, figure 2" /></a>

Parallel

In a PARALLEL circuit, the current splits and divides down each branch of the circuit.

<img src="/img/notes/02/6.jpg" alt="Circuits, figure 3" /></a>

<h2 id="potential-difference-voltage">Potential Difference (Voltage)</h2>

Potential difference refers to the difference in charge between the positive and negative ends of the cell/battery. The bigger the potential difference, the bigger the force on the electrons – pushing them around the circuit.

<img src="/img/notes/02/7.jpg" alt="Circuits, figure 1" /></a>

Potential Difference is measured in Volts (and commonly called voltage). It is measured using a voltmeter which is placed in parallel with the component across which it is measuring the voltage.

The relationship between energy, potential difference and charge is described by this equation (you DO need to remember this for your exam):

<h3 class="ql-align-center">E = VQ</h3>

E = Energy transferred (Joules, J)

V = Potential difference (Volts, V)

Q = flow of charge (Coulombs, C)

Worked Example

The energy transferred to a bulb is 360J when 64C of charge passes through it. Calculate the potential difference across the bulb.

E=VQ

V = E ÷ Q

V = 360 ÷ 64

V = 50V

Series

In a SERIES circuit, the voltage is shared out between each component.

<img src="/img/notes/02/8.jpg" alt="Circuits, figure 2" /></a>

Parallel﻿

In a PARALLEL circuit, each branch of the circuit receives the same voltage as the power supply.

<img src="/img/notes/02/9.jpg" alt="Circuits, figure 3" /></a>

<h2 id="summary">Summary</h2>

When analysing circuits it is very important to remember the ‘laws’ for the behaviour of potential difference and current in series and parallel circuits:

Current:

<ol>
 <li>In a SERIES circuit, the current is always the same, no matter where you place the ammeter</li>
 <li>In a PARALLEL circuit, the current splits and divides down each branch of the circuit</li>
</ol>

Potential Difference:

<ol>
 <li>In a SERIES circuit, the voltage is shared out between each component</li>
 <li>In a PARALLEL circuit, each branch of the circuit receives the same voltage as the power supply</li>
</ol>

<dl>
	<dt>Calculate the charge if 5A of current flows for 3s. </dt>
	<dd id="Summary0" class="js-click-to-reveal">15</dd>
	<dt>Calculate the current if 75C of current flows for 25s.</dt>
	<dd id="Summary1" class="js-click-to-reveal">3</dd>
	<dt>Calculate the energy supplied by a 6V torch battery if 1500C of charge flows.</dt>
	<dd id="Summary2" class="js-click-to-reveal">9000</dd>
	<dt>Calculate the charge that flows if 4800J of energy is supplied in a circuit at 240V? </dt>
	<dd id="Summary3" class="js-click-to-reveal">20</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Circuits</h1>
</header>

<main class="blog-post__content">
	<h2 id="circuit-symbols">Circuit Symbols</h2>

	All circuit diagrams use a set of established symbols. You need to be familiar with the circuit symbols below to understand the circuit diagrams that you may encounter in your exam.

	<a href="/img/notes/02/1.jpg" target="_blank"><img src="/img/notes/02/1.jpg" alt="Circuits, figure 1" /></a>

	<h2 id="series-and-parallel">Series and Parallel</h2>

	Circuits can be categorized as series or parallel.

	Series Circuits

	<a href="/img/notes/02/2.jpg" target="_blank"><img src="/img/notes/02/2.jpg" alt="Circuits, figure 1" /></a>

	In a series circuit:

	<ol>
		<li>There is only one path around the circuit</li>
		<li>If one component breaks, all the other components will stop working</li>
		<li>More bulbs in series will cause the brightness of all the bulbs to decrease</li>
		<li>Switches will control all the bulbs together</li>
	</ol>

	Parallel Circuits

	<a href="/img/notes/02/3.jpg" target="_blank"><img src="/img/notes/02/3.jpg" alt="Circuits, figure 2" /></a>

	In a parallel circuit:

	<ol>
		<li>There is more than one path around the circuit</li>
		<li>If one component breaks, the others stay on</li>
		<li>More bulbs added in parallel will be the same brightness as the original bulb</li>
		<li>Switches (on branches) will control bulbs individually</li>
	</ol>

	<h2 id="current">Current</h2>

	Current is the flow of electrons (charged particles) around a circuit. Electrons are repelled from the negative end of the cell and attracted to the positive end.

	Current is measured using an ammeter which is connected in series with the circuit.

	<a href="/img/notes/02/4.jpg" target="_blank"><img src="/img/notes/02/4.jpg" alt="Circuits, figure 1" /></a>

	The flow of charge can be calculated using this equation (you need to remember this for your exam):

	<h3 class="ql-align-center">Q = It</h3>

	Q = flow of charge (Coulombs, C)

	I = current (Amps, A)

	t = time (s)

	Worked Example:

	A charge of 16C passes through a bulb in 5s. Calculate the current through the bulb.

	Q = It

	I = Q ÷ t

	I = 16 ÷ 5

	I = 3.2A

	Series

	In a series circuit, the current is always the same, no matter where you place the ammeter.

	<a href="/img/notes/02/5.jpg" target="_blank"><img src="/img/notes/02/5.jpg" alt="Circuits, figure 2" /></a>

	Parallel

	In a parallel circuit, the current splits and divides down each branch of the circuit.

	<a href="/img/notes/02/6.jpg" target="_blank"><img src="/img/notes/02/6.jpg" alt="Circuits, figure 3" /></a>

	<h2 id="potential-difference-voltage">Potential Difference (Voltage)</h2>

	Potential difference refers to the difference in charge between the positive and negative ends of the cell/battery. The bigger the potential difference, the bigger the force on the electrons – pushing them around the circuit.

	<a href="/img/notes/02/7.jpg" target="_blank"><img src="/img/notes/02/7.jpg" alt="Circuits, figure 1" /></a>

	Potential Difference is measured in Volts (and commonly called voltage). It is measured using a voltmeter which is placed in parallel with the component across which it is measuring the voltage.

	The relationship between energy, potential difference, and charge is described by this equation (you need to remember this for your exam):

	<h3 class="ql-align-center">E = VQ</h3>

	E = Energy transferred (Joules, J)

	V = Potential difference (Volts, V)

	Q = flow of charge (Coulombs, C)

	Worked Example:

	The energy transferred to a bulb is 360J when 64C of charge passes through it. Calculate the potential difference across the bulb.

	E=VQ

	V = E ÷ Q

	V = 360 ÷ 64

	V = 5.625V

	Series

	In a series circuit, the voltage is shared out between each component.

	<a href="/img/notes/02/8.jpg" target="_blank"><img src="/img/notes/02/8.jpg" alt="Circuits, figure 2" /></a>

	Parallel

	In a parallel circuit, each branch of the circuit receives the same voltage as the power supply.

	<a href="/img/notes/02/9.jpg" target="_blank"><img src="/img/notes/02/9.jpg" alt="Circuits, figure 3" /></a>

	<h2 id="summary">Summary</h2>

	When analyzing circuits, it is very important to remember the ‘laws’ for the behavior of potential difference and current in series and parallel circuits:

	Current:

	<ol>
		<li>In a series circuit, the current is always the same, no matter where you place the ammeter</li>
		<li>In a parallel circuit, the current splits and divides down each branch of the circuit</li>
	</ol>

	Potential Difference:

	<ol>
		<li>In a series circuit, the voltage is shared out between each component</li>
		<li>In a parallel circuit, each branch of the circuit receives the same voltage as the power supply</li>
	</ol>

	<dl>
		<dt>Calculate the charge if 5A of current flows for 3s. </dt>
		<dd id="Summary0" class="js-click-to-reveal">15C</dd>
		<dt>Calculate the current if 75C of charge flows for 25s.</dt>
		<dd id="Summary1" class="js-click-to-reveal">3A</dd>
		<dt>Calculate the energy supplied by a 6V torch battery if 1500C of charge flows.</dt>
		<dd id="Summary2" class="js-click-to-reveal">9000J</dd>
		<dt>Calculate the charge that flows if 4800J of energy is supplied in a circuit at 240V? </dt>
		<dd id="Summary3" class="js-click-to-reveal">20C</dd>
	</dl>
</main>

Circuits

<header>
			<h1 class="blog-post__title">Analysing Circuits</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="analysing-circuits">Analysing Circuits</h2>

In the last couple of lessons we have learned about current, potential difference (voltage) and resistance in series and parallel circuits. Students tend to start finding circuits difficult when these three things are combined so we’ll work through some examples in this lesson so you can get the hang of it.

Any circuit problem can be solved by using a combination of Ohm’s law, the current laws and the voltage laws.

Ohms law:

voltage = current x resistance

__Current laws: __

Current is constant in a series circuit

Current divides down the branches of a parallel circuit

Voltage laws:

Voltage is shared between components in a series circuit

Each branch of a parallel circuit receives the same voltage as the power supply

<h2 id="worked-examples">Worked Examples</h2>

<h2 class="ql-align-center">Worked Example 1</h2>

Calculate the voltmeter readings and the resistance of the motor

<img src="/img/notes/02/1-1.png" alt="Analysing Circuits, figure 1" /></a>

Steps to answer this question:

<ol>
 <li>Work out whether you are dealing with a series or parallel circuit – in this case we have a SERIES circuit (the voltmeters don’t count as part of the circuit.</li>
 <li>Voltage 1: We want to use the equation V=IR</li>
 <li>In a series circuit, the current is the same everywhere in the circuit, so we know that the current flowing through the bulb is 0.3A</li>
 <li>The resistance of the bulb is labelled as 16Ω</li>
 <li>V = IR = 0.3 x 16 = 8V</li>
 <li>Voltage 2: We want to use the equation V=IR</li>
 <li>In a series circuit, the current is the same everywhere in the circuit, so we know that the current flowing through the resistor is 0.3A</li>
 <li>The resistance of the resistor is labelled as 4Ω</li>
 <li>V = IR = 0.3 x 4 = 2V</li>
 <li>Voltage 3: We want to use the equation V=IR but we do not have enough information to use it for this voltmeter – we know the current, but the resistance has not been labelled.</li>
 <li>At this stage, DON’ PANIC! If we can’t use the equation, there must be another way</li>
 <li>The voltage law for series circuits says that the voltage supplied by the battery will be shared out between the components. Because we know the voltages of the other two components (and the power supply) we can work out V3</li>
 <li>V(battery) = V1 +V2 +V3</li>
 <li>12 = 4.8 + 1.2 + V3</li>
 <li>V3 = 6V</li>
 <li>Resistance of motor</li>
 <li>Rearrange V = IR to R = V/I</li>
 <li>R = 6/0.3 = 20 Ω</li>
</ol>

Don’t panic and work your way through Ohm’s law and the current and voltage laws until you have all the information you need.

<h2 class="ql-align-center">Worked Example 2</h2>

In the circuit shown, the potential difference across the 4Ω resistor is 8V

<img src="/img/notes/02/2-1.png" alt="Analysing Circuits, figure 2" /></a>

What is the current through the 4 Ω resistor?

Rearrange the equation V=IR to I=V/R

I = 8/4 = 2A

What is the current through the 3 Ω resistor?

We do not know the voltage across the 3 Ω resistor so cannot use the equation.

We do know that this is a series circuit, and in a series circuit, current is the same everywhere in the circuit.

As we have just calculated in part (a), the current through the other resistor is 2A, therefore the current through this resistor (and anywhere else in the circuit) is 2A

What is the p.d. across the 3 Ω resistor?

Use the equation V=IR

V = IR = 2x3 = 6V

What is the p.d. of the battery?

We do not know the resistance of the battery so cannot use the equation.

We do know that this is a series circuit and, in a series circuit, the potential difference (voltage) of the power supply is shared between the components.

As we know the voltages across each resistor, we can simply add those together.

V(battery) = 6 + 8 = 14V

<h3 id="remember">Remember:</h3>

Ohms law:

voltage = current x resistance

Current laws:

Current is constant in a series circuit

Current divides down the branches of a parallel circuit

Voltage laws:

Voltage is shared between components in a series circuit

Each branch of a parallel circuit receives the same voltage as the power supply

		</main>

<header>
	<h1 class="blog-post__title">Analyzing Circuits</h1>
</header>

<main class="blog-post__content">
	<h2 id="analyzing-circuits">Analyzing Circuits</h2>

	In the last couple of lessons, we have learned about current, potential difference (voltage), and resistance in series and parallel circuits. Students tend to find circuits difficult when these three things are combined, so we will work through some examples in this lesson to help you understand it better.

	Any circuit problem can be solved by using a combination of Ohm's law, the current laws, and the voltage laws.

	Ohm's law:

	voltage = current x resistance

	Current laws:

	Current is constant in a series circuit.

	Current divides down the branches of a parallel circuit.

	Voltage laws:

	Voltage is shared between components in a series circuit.

	Each branch of a parallel circuit receives the same voltage as the power supply.

	<h2 id="worked-examples">Worked Examples</h2>

	<h2 class="ql-align-center">Worked Example 1</h2>

	Calculate the voltmeter readings and the resistance of the motor.

	<img src="/img/notes/02/1-1.png" alt="Analysing Circuits, figure 1" />

	Steps to answer this question:

	<ol>
		<li>Work out whether you are dealing with a series or parallel circuit – in this case, we have a SERIES circuit (the voltmeters don't count as part of the circuit).</li>
		<li>Voltage 1: We want to use the equation V=IR.</li>
		<li>In a series circuit, the current is the same everywhere in the circuit, so we know that the current flowing through the bulb is 0.3A.</li>
		<li>The resistance of the bulb is labeled as 16Ω.</li>
		<li>V = IR = 0.3 x 16 = 8V.</li>
		<li>Voltage 2: We want to use the equation V=IR.</li>
		<li>In a series circuit, the current is the same everywhere in the circuit, so we know that the current flowing through the resistor is 0.3A.</li>
		<li>The resistance of the resistor is labeled as 4Ω.</li>
		<li>V = IR = 0.3 x 4 = 1.2V.</li>
		<li>Voltage 3: We want to use the equation V=IR, but we do not have enough information to use it for this voltmeter – we know the current, but the resistance has not been labeled.</li>
		<li>At this stage, DON'T PANIC! If we can't use the equation, there must be another way.</li>
		<li>The voltage law for series circuits says that the voltage supplied by the battery will be shared out between the components. Because we know the voltages of the other two components (and the power supply), we can work out V3.</li>
		<li>V(battery) = V1 + V2 + V3</li>
		<li>12 = 8 + 1.2 + V3</li>
		<li>V3 = 2.8V</li>
		<li>Resistance of motor:</li>
		<li>Rearrange V = IR to R = V/I.</li>
		<li>R = 2.8/0.3 = 9.33 Ω</li>
	</ol>

	Don't panic and work your way through Ohm's law and the current and voltage laws until you have all the information you need.

	<h2 class="ql-align-center">Worked Example 2</h2>

	In the circuit shown, the potential difference across the 4Ω resistor is 8V.

	<img src="/img/notes/02/2-1.png" alt="Analysing Circuits, figure 2" />

	What is the current through the 4 Ω resistor?

	Rearrange the equation V=IR to I=V/R.

	I = 8/4 = 2A.

	What is the current through the 3 Ω resistor?

	We do not know the voltage across the 3 Ω resistor, so we cannot use the equation.

	We do know that this is a series circuit, and in a series circuit, current is the same everywhere in the circuit.

	As we have just calculated in part (a), the current through the other resistor is 2A; therefore, the current through this resistor (and anywhere else in the circuit) is 2A.

	What is the p.d. across the 3 Ω resistor?

	Use the equation V=IR.

	V = IR = 2 x 3 = 6V.

	What is the p.d. of the battery?

	We do not know the resistance of the battery, so we cannot use the equation.

	We do know that this is a series circuit, and in a series circuit, the potential difference (voltage) of the power supply is shared between the components.

	As we know the voltages across each resistor, we can simply add those together.

	V(battery) = 6 + 8 = 14V.

	<h3 id="remember">Remember:</h3>

	Ohm's law:

	voltage = current x resistance

	Current laws:

	Current is constant in a series circuit.

	Current divides down the branches of a parallel circuit.

	Voltage laws:

	Voltage is shared between components in a series circuit.

	Each branch of a parallel circuit receives the same voltage as the power supply.
</main>

Analysing Circuits

<header>
			<h1 class="blog-post__title">Particles</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="density">Density</h2>

The density of a substance is defined as its mass per unit volume. If two objects are the same size but different densities, the more dense object will be heavier.

Density can be calculated using the following equation (you DO need to remember this equation for your exam):

<h1 class="ql-align-center">ρ = m ÷ v</h1>

ρ = density (kg/m3)

m = mass (kg)

v = volume (m3)

Worked Example

A wooden post has a volume of 0.025m3 and a mass of 20kg. Calculate its density.

ρ = m ÷ v

ρ = 20 ÷ 0.025

ρ = 800kg/m3

Density can have units of kg/m3 or g/cm3

Converting units:

<ol>
 <li>1 kg = 1000g</li>
 <li>1m = 100cm</li>
 <li>1m3 = 1,000,000 cm3</li>
 <li>1000 kg/m3 = 1,000,000g ÷ 1,000,000cm3 = 1g/cm3</li>
</ol>

<h2 id="states-of-matter">States of Matter</h2>

There are 3 states of matter:

<ol>
 <li>Solid</li>
 <li>Liquid</li>
 <li>Gas</li>
</ol>

They are defined by the arrangement and movement of their particles.

Solids

<img src="/img/notes/02/solid.png" alt="Particles, figure 1" /></a>

<ol>
 <li>Particles tightly packed together</li>
 <li>Vibrate in fixed positions</li>
 <li>Fixed shape</li>
 <li>Fixed volume (can not be compressed)</li>
 <li>High density</li>
</ol>

Liquids

<img src="/img/notes/02/liquid.png" alt="Particles, figure 2" /></a>

<ol>
 <li>Particles close together</li>
 <li>Move around randomly</li>
 <li>No fixed shape</li>
 <li>Fixed volume (can not be compressed)</li>
</ol>

Gases

<img src="/img/notes/02/gas.png" alt="Particles, figure 3" /></a>

<ol>
 <li>Particles move around randomly at high speeds</li>
 <li>Particles far apart</li>
 <li>No fixed shape</li>
 <li>No fixed volume (can be compressed)</li>
 <li>Low density</li>
</ol>

<h2 id="changes-of-state">Changes of State</h2>

<img src="/img/notes/02/changes-of-state.png" alt="Particles, figure 1" /></a>

When a substance changes state, energy is transferred to or from the substance. Thermal energy is transferred to a solid to cause it to melt. Thermal energy is transferred from a liquid, causing it to freeze.

When a substance changes state, the number of particles remains the same. Therefore the mass of the substance remains the same. This is known as conservation of mass.

As a substance is heated, it’s particles gain kinetic energy allowing them to break free of their positions and melt or evaporate/boil. As a substance cools, it’s particles lose kinetic energy.

<img src="/img/notes/02/Heating-Curve.png" alt="Particles, figure 2" /></a>

As a substance changes state, it’s temperature remains constant even though thermal energy is being transferred to it. This energy is called latent heat.

<h2 id="internal-energy">Internal Energy</h2>

The energy stored in the particles of a substance is called internal energy. Increasing the temperature of a substance increases it’s internal energy.

The internal energy depends on:

<ol>
 <li>The kinetic energy of each particle</li>
 <li>The potential energy of the particles based on the distance between them</li>
 <li>Video 1</a></li>
 <li>Video 2</a></li>
</ol>

Internal Energy in solids, liquids and gases:

Solids

<ol>
 <li>Strong forces of attraction between particles</li>
 <li>Particles vibrate in fixed positions</li>
 <li>When heated, particles vibrate with more kinetic energy</li>
 <li>If heated enough, the solid melts – the particles break free of their positions</li>
</ol>

Liquids

<ol>
 <li>Weaker forces of attraction between particles – enough to keep them together, but not enough to keep them in fixed positions</li>
 <li>When heated, particles move faster</li>
 <li>If heated enough, the particles gain enough energy to break away from the other particles, becoming a gas</li>
</ol>

<h3 id="gases">Gases</h3>

<ol>
 <li>Insignificant forces of attraction between particles</li>
 <li>Particles move around randomly at high speeds, colliding with each other and the sides of the container</li>
 <li>When heated, the particles gain kinetic energy and move faster</li>
 <li>They collide more often and with more force, increasing pressure</li>
</ol>

<h2 id="latent-heat">Latent Heat</h2>

When an object is changing state, it’s temperature does not increase even though it is being heated/cooled. Latent heat is the energy needed for a substance to change state.

<ol>
 <li>Specific Latent Heat of fusion is the amount of energy required to change 1kg of the substance from solid to liquid</li>
 <li>Specific Latent Heat of vaporisation is the amount of energy required to change 1kg of the substance from liquid to gas</li>
</ol>

Specific Latent heat can be calculated using this equation (you do NOT need to remember this equation for your exam):

<ol>
 <li>L = Specific Latent Heat (J/kg)</li>
 <li>E = Energy (J)</li>
 <li>m = mass (kg)</li>
</ol>

Worked Example

Calculate the mass of ice lost from an iceberg melting, if the energy supplied was 835 000 000J.

Latent heat of fusion = 334 000 J/Kg

E=mL

m=E÷L

m=835,000,000 ÷ 334,000

m= 2500kg

Measuring the specific latent heat of fusion of ice:

<ol>
 <li>Place ice in a funnel and collect the melted ice (water) that flows through the funnel in a measuring cylinder.</li>
 <li>Measure the mass of water collected in 10 minutes.</li>
 <li>Repeat but add an immersion heater to the ice.</li>
 <li>Measure the mass of water collected in 10 minutes with the heater on</li>
 <li>The difference between those two masses is used as m in the equation</li>
 <li>Calculate the specific latent heat of fusion using the equation</li>
</ol>

Measuring the specific latent heat of vaporisation of water:

<ol>
 <li>Heat water to boiling point on an electronic balance.</li>
 <li>The mass change on the balance as the water evaporates is used as m in the equation</li>
</ol>

<h2 id="required-practical--measuring-density">Required Practical – Measuring Density</h2>

<img src="/img/notes/02/block.png" alt="Particles, figure 1" /></a>

To calculate density for a regular shaped solid:

<ol>
 <li>Measure mass on balance</li>
 <li>Calculate volume mathematically (length x width x height)</li>
 <li>Calculate density = mass ÷ volume</li>
</ol>

<img src="/img/notes/02/rock.png" alt="Particles, figure 2" /></a>

To calculate density for an irregular solid:

<ol>
 <li>Measure mass on balance</li>
 <li>Measure volume using displacement – place the object in water and measure the amount of water displaced</li>
 <li>Calculate density = mass ÷ volume</li>
</ol>

<img src="/img/notes/02/water.png" alt="Particles, figure 3" /></a>

To calculate density for a liquid:

<ol>
 <li>Measure mass on balance (total mass – mass of container)</li>
 <li>Measure volume using measuring cylinder</li>
 <li>Calculate density = mass ÷ volume</li>
</ol>

Possible causes of error in these investigations include:

<ol>
 <li>Inaccurate measurement of mass</li>
 <li>Inaccurate measurement of length etc of regular shaped solid</li>
 <li>Inaccurate measurement of displaced water</li>
</ol>

<h2 id="gas-pressure">Gas Pressure</h2>

<h3 id="brownian-motion">Brownian Motion</h3>

Individual molecules are too small to see directly but their motion can be observed by their effect on other particles. Particles in a gas move randomly. They move very fast. They collide with each other and the sides of the container. This is called Brownian motion.

<img src="/img/notes/02/ezgif.com-resize-2.gif" alt="Particles, figure 1" /></a>

Gas Pressure and Temperature

Increasing the temperature of a gas will increase the pressure as the particles move faster, causing more frequent collisions. This means that the pressure will increase (if the volume remains constant).

<img src="/img/notes/02/pressure-temp.png" alt="Particles, figure 2" /></a>

Pressure and Volume

The same amount of air molecules in a smaller volume will exert more pressure as there will be more collisions:

<img src="/img/notes/02/pressure-volume-1004x1024.jpg" alt="Particles, figure 3" /></a>

<h2 id="boyles-law">Boyle’s Law</h2>

Gas pressure is inversely proportional to volume

P x V = constant

P1V1 = P2V2

(you do NOT need to remember this equation for your exam)

<dl>
	<dt>What is the density of an object with mass 45kg and volume 5m3?</dt>
	<dd id="Boyles-Law0" class="js-click-to-reveal">9</dd>
	<dt>What is the mass of an object with volume 4m3 and density 5450kg/m3?</dt>
	<dd id="Boyles-Law1" class="js-click-to-reveal">21800</dd>
	<dt>What is the volume of an object with mass 420kg and density 140kg/m3?</dt>
	<dd id="Boyles-Law2" class="js-click-to-reveal">3</dd>
	<dt>A jeweller melts 0.5kg of gold to pour into a mould. Calculate how much energy was released as the gold solidified. (Latent heat of fusion of gold = 88000J/kg)</dt>
	<dd id="Boyles-Law3" class="js-click-to-reveal">44000</dd>
	<dt>A kettle fails to switch off and boils for 5 minutes, wasting 600 000 J of energy. Calculate the mass of water lost during this time. (Latent heat of vaporisation of water = 2,260,000J/kg)</dt>
	<dd id="Boyles-Law4" class="js-click-to-reveal">0.265</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Particles</h1>
</header>

<main class="blog-post__content">
	<h2 id="density">Density</h2>

	The density of a substance is defined as its mass per unit volume. If two objects are the same size but have different densities, the more dense object will be heavier.

	Density can be calculated using the following equation (you DO need to remember this equation for your exam):

	<h1 class="ql-align-center">ρ = m ÷ v</h1>

	ρ = density (kg/m3)

	m = mass (kg)

	v = volume (m3)

	Worked Example

	A wooden post has a volume of 0.025m3 and a mass of 20kg. Calculate its density.

	ρ = m ÷ v

	ρ = 20 ÷ 0.025

	ρ = 800kg/m3

	Density can have units of kg/m3 or g/cm3.

	Converting units:

	<ol>
		<li>1 kg = 1000g</li>
		<li>1m = 100cm</li>
		<li>1m3 = 1,000,000 cm3</li>
		<li>1000 kg/m3 = 1,000,000g ÷ 1,000,000cm3 = 1g/cm3</li>
	</ol>

	<h2 id="states-of-matter">States of Matter</h2>

	There are 3 states of matter:

	<ol>
		<li>Solid</li>
		<li>Liquid</li>
		<li>Gas</li>
	</ol>

	They are defined by the arrangement and movement of their particles.

	Solids

	<a href="/img/notes/02/solid.png" target="_blank"><img class="img-30" src="/img/notes/02/solid.png" alt="Particles, figure 1" /></a>

	<ol>
		<li>Particles tightly packed together</li>
		<li>Vibrate in fixed positions</li>
		<li>Fixed shape</li>
		<li>Fixed volume (cannot be compressed)</li>
		<li>High density</li>
	</ol>

	Liquids

	<a href="/img/notes/02/liquid.png" target="_blank"><img class="img-30" src="/img/notes/02/liquid.png" alt="Particles, figure 2" /></a>

	<ol>
		<li>Particles close together</li>
		<li>Move around randomly</li>
		<li>No fixed shape</li>
		<li>Fixed volume (cannot be compressed)</li>
	</ol>

	Gases

	<a href="/img/notes/02/gas.png" target="_blank"><img class="img-30" src="/img/notes/02/gas.png" alt="Particles, figure 3" /></a>

	<ol>
		<li>Particles move around randomly at high speeds</li>
		<li>Particles far apart</li>
		<li>No fixed shape</li>
		<li>No fixed volume (can be compressed)</li>
		<li>Low density</li>
	</ol>

	<h2 id="changes-of-state">Changes of State</h2>

	<a href="/img/notes/02/changes-of-state.png" target="_blank"><img src="/img/notes/02/changes-of-state.png" alt="Particles, figure 1" /></a>

	When a substance changes state, energy is transferred to or from the substance. Thermal energy is transferred to a solid to cause it to melt. Thermal energy is transferred from a liquid, causing it to freeze.

	When a substance changes state, the number of particles remains the same. Therefore, the mass of the substance remains the same. This is known as conservation of mass.

	As a substance is heated, its particles gain kinetic energy, allowing them to break free of their positions and melt or evaporate/boil. As a substance cools, its particles lose kinetic energy.

	<a href="/img/notes/02/Heating-Curve.png" target="_blank"><img src="/img/notes/02/Heating-Curve.png" alt="Particles, figure 2" /></a>

	As a substance changes state, its temperature remains constant even though thermal energy is being transferred to it. This energy is called latent heat.

	<h2 id="internal-energy">Internal Energy</h2>

	The energy stored in the particles of a substance is called internal energy. Increasing the temperature of a substance increases its internal energy.

	The internal energy depends on:

	<ol>
		<li>The kinetic energy of each particle</li>
		<li>The potential energy of the particles based on the distance between them</li>
		<li><a href="https://www.youtube.com/watch?v=aDXQBE4r65Y" target="_blank">Video 1</a></li>
		<li><a href="https://www.youtube.com/watch?v=ndw9XYA4iF0" target="_blank">Video 2</a></li>
	</ol>

	Internal Energy in solids, liquids, and gases:

	Solids

	<ol>
		<li>Strong forces of attraction between particles</li>
		<li>Particles vibrate in fixed positions</li>
		<li>When heated, particles vibrate with more kinetic energy</li>
		<li>If heated enough, the solid melts – the particles break free of their positions</li>
	</ol>

	Liquids

	<ol>
		<li>Weaker forces of attraction between particles – enough to keep them together, but not enough to keep them in fixed positions</li>
		<li>When heated, particles move faster</li>
		<li>If heated enough, the particles gain enough energy to break away from the other particles, becoming a gas</li>
	</ol>

	<h3 id="gases">Gases</h3>

	<ol>
		<li>Insignificant forces of attraction between particles</li>
		<li>Particles move around randomly at high speeds, colliding with each other and the sides of the container</li>
		<li>When heated, the particles gain kinetic energy and move faster</li>
		<li>They collide more often and with more force, increasing pressure</li>
	</ol>

	<h2 id="latent-heat">Latent Heat</h2>

	When an object is changing state, its temperature does not increase even though it is being heated/cooled. Latent heat is the energy needed for a substance to change state.

	<ol>
		<li>Specific Latent Heat of fusion is the amount of energy required to change 1kg of the substance from solid to liquid</li>
		<li>Specific Latent Heat of vaporisation is the amount of energy required to change 1kg of the substance from liquid to gas</li>
	</ol>

	Specific Latent heat can be calculated using this equation (you do NOT need to remember this equation for your exam):

	<ol>
		<li>L = Specific Latent Heat (J/kg)</li>
		<li>E = Energy (J)</li>
		<li>m = mass (kg)</li>
	</ol>

	Worked Example

	Calculate the mass of ice lost from an iceberg melting if the energy supplied was 835,000,000J.

	Latent heat of fusion = 334,000 J/Kg

	E = mL

	m = E ÷ L

	m = 835,000,000 ÷ 334,000

	m = 2500kg

	Measuring the specific latent heat of fusion of ice:

	<ol>
		<li>Place ice in a funnel and collect the melted ice (water) that flows through the funnel in a measuring cylinder.</li>
		<li>Measure the mass of water collected in 10 minutes.</li>
		<li>Repeat but add an immersion heater to the ice.</li>
		<li>Measure the mass of water collected in 10 minutes with the heater on.</li>
		<li>The difference between those two masses is used as m in the equation.</li>
		<li>Calculate the specific latent heat of fusion using the equation.</li>
	</ol>

	Measuring the specific latent heat of vaporisation of water:

	<ol>
		<li>Heat water to boiling point on an electronic balance.</li>
		<li>The mass change on the balance as the water evaporates is used as m in the equation.</li>
	</ol>

	<h2 id="required-practical--measuring-density">Required Practical – Measuring Density</h2>

	<a href="/img/notes/02/block.png" target="_blank"><img class="img-30" src="/img/notes/02/block.png" alt="Particles, figure 1" /></a>

	To calculate density for a regular shaped solid:

	<ol>
		<li>Measure mass on a balance</li>
		<li>Calculate volume mathematically (length x width x height)</li>
		<li>Calculate density = mass ÷ volume</li>
	</ol>

	<a href="/img/notes/02/rock.png" target="_blank"><img class="img-30" src="/img/notes/02/rock.png" alt="Particles, figure 2" /></a>

	To calculate density for an irregular solid:

	<ol>
		<li>Measure mass on a balance</li>
		<li>Measure volume using displacement – place the object in water and measure the amount of water displaced</li>
		<li>Calculate density = mass ÷ volume</li>
	</ol>

	<a href="/img/notes/02/water.png" target="_blank"><img class="img-30" src="/img/notes/02/water.png" alt="Particles, figure 3" /></a>

	To calculate density for a liquid:

	<ol>
		<li>Measure mass on a balance (total mass – mass of container)</li>
		<li>Measure volume using a measuring cylinder</li>
		<li>Calculate density = mass ÷ volume</li>
	</ol>

	Possible causes of error in these investigations include:

	<ol>
		<li>Inaccurate measurement of mass</li>
		<li>Inaccurate measurement of length, etc., of a regular shaped solid</li>
		<li>Inaccurate measurement of displaced water</li>
	</ol>

	<h2 id="gas-pressure">Gas Pressure</h2>

	<h3 id="brownian-motion">Brownian Motion</h3>

	Individual molecules are too small to see directly, but their motion can be observed by their effect on other particles. Particles in a gas move randomly. They move very fast. They collide with each other and the sides of the container. This is called Brownian motion.

	<a href="/img/notes/02/ezgif.com-resize-2.gif" target="_blank"><img src="/img/notes/02/ezgif.com-resize-2.gif" alt="Particles, figure 1" /></a>

	Gas Pressure and Temperature

	Increasing the temperature of a gas will increase the pressure as the particles move faster, causing more frequent collisions. This means that the pressure will increase (if the volume remains constant).

	<a href="/img/notes/02/pressure-temp.png" target="_blank"><img src="/img/notes/02/pressure-temp.png" alt="Particles, figure 2" /></a>

	Pressure and Volume

	The same amount of air molecules in a smaller volume will exert more pressure as there will be more collisions:

	<a href="/img/notes/02/pressure-volume-1004x1024.jpg" target="_blank"><img src="/img/notes/02/pressure-volume-1004x1024.jpg" alt="Particles, figure 3" /></a>

	<h2 id="boyles-law">Boyle’s Law</h2>

	Gas pressure is inversely proportional to volume

	P x V = constant

	P1V1 = P2V2

	(you do NOT need to remember this equation for your exam)

	<dl>
		<dt>What is the density of an object with a mass of 45kg and a volume of 5m3?</dt>
		<dd id="Boyles-Law0" class="js-click-to-reveal">9</dd>
		<dt>What is the mass of an object with a volume of 4m3 and a density of 5450kg/m3?</dt>
		<dd id="Boyles-Law1" class="js-click-to-reveal">21800</dd>
		<dt>What is the volume of an object with a mass of 420kg and a density of 140kg/m3?</dt>
		<dd id="Boyles-Law2" class="js-click-to-reveal">3</dd>
		<dt>A jeweler melts 0.5kg of gold to pour into a mold. Calculate how much energy was released as the gold solidified. (Latent heat of fusion of gold = 88000J/kg)</dt>
		<dd id="Boyles-Law3" class="js-click-to-reveal">44000</dd>
		<dt>A kettle fails to switch off and boils for 5 minutes, wasting 600,000 J of energy. Calculate the mass of water lost during this time. (Latent heat of vaporisation of water = 2,260,000J/kg)</dt>
		<dd id="Boyles-Law4" class="js-click-to-reveal">0.265</dd>
	</dl>
</main>

Particles

Particle Model of Matter

<header>
			<h1 class="blog-post__title">Radioactive Atoms</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="rutherford-geiger-marsden-gold-foil-experiment">Rutherford-Geiger-Marsden (Gold Foil) Experiment</h2>

In this experiment, positively charged aalpha particles were directed at gold foil with a fluorescent screen to detect the alpha particles after they interacted with the foil.

<img src="/img/notes/02/Geiger-Marsden_experiment.svg-300x195.png" alt="Radioactive Atoms, figure 1" /></a>

Most of the alpha particles passed straight through the foil, with others passing through on a deflected path and a smaller amount bouncing back off the foil.

This led to a number of conclusions:

<ol>
 <li>Most of the atom is empty space (because most alpha particles passed through)</li>
 <li>Most of the mass is concentrated in a small space (nucleus)</li>
 <li>Nucleus has a positive charge (because it repelled the positive alpha particles)</li>
 <li>Nucleus is surrounded by orbiting electrons</li>
</ol>

<img src="/img/notes/02/rutherford-300x263.png" alt="Radioactive Atoms, figure 2" /></a>

<h2 id="scientific-method">Scientific Method</h2>

The scientific method describes how theories are developed and modified:

<ol>
 <li>Evidence is collected from an experiment</li>
 <li>A theory is developed to explain the evidence</li>
 <li>The theory is tested with further investigations/results</li>
 <li>The theory is modified if necessary based on the further evidence</li>
</ol>

You use this process regularly without realising it! For example:

<ol>
 <li>Light bulb does not come on when you press the switch (evidence)</li>
 <li>The bulb might be broken (theory)</li>
 <li>Replace bulb and try again (testing theory)</li>
 <li>If new bulb works, your theory was proved to be correct</li>
 <li>If new bulb does not work, your theory needs to be modified (eg there may be a problem with the wiring)</li>
</ol>

<h2 id="isotopes">Isotopes</h2>

The atomic number for an element is the number of protons in the nucleus of that element. This does not change for a particular element. If there are a different number of protons it is a different element.

The mass number is the number of particles in the nucleus (protons and neutrons) for an element. The mass number for a particular element can vary as the number of neutrons can be different (still the same element).

<img src="/img/notes/02/1-2-300x150.png" alt="Radioactive Atoms, figure 1" /></a>

Isotopes have the same number of protons as the original element but different numbers of neutrons.

Some isotopes are unstable/radioactive. These unstable isotopes will decay, emitting radiation from the nucleus.

Hydrogen

For example, most hydrogen atoms have 1 proton and 1 electron:

<img src="/img/notes/02/hydrogen-isotopes.png" alt="Radioactive Atoms, figure 2" /></a>

But two other isotopes of hydrogen also exist:

Deuterium (1 proton and 1 neutron)

Tritium (1 proton and 2 neutrons)

Carbon

<img src="/img/notes/02/carbon-isotopes.png" alt="Radioactive Atoms, figure 3" /></a>

Most Carbon exists as Carbon-12 (6 protons &amp; 6 neutrons)

Carbon-11 is an isotope of carbon that has 6 protons (because carbon always has 6 protons) and 5 neutrons (because the mass number is 11)

Other isotopes of carbon also exist. Some isotopes are unstable (radioactive).

For isotopes:

<ol>
 <li>Mass number is different</li>
 <li>Atomic number is the same</li>
</ol>

<h2 id="radioactive-decay">Radioactive Decay</h2>

When an unstable isotope decays, it releases radiation from the nucleus. The remaining nucleus will have different numbers of particles.

There are three types of radiation – alpha, beta and gamma:

<img src="/img/notes/02/types-of-radiation.png" alt="Radioactive Atoms, figure 1" /></a>

<h2 id="developing-the-model-of-the-atom">Developing the Model of the Atom</h2>

<img src="/img/notes/02/sphere-300x300.png" alt="Radioactive Atoms, figure 1" /></a>

<ol>
 <li>The Greek philosopher Democritus named the smallest (indivisible) parts of a substance ‘atoms’</li>
 <li>In 1897 electrons were discovered. This led to the ‘plum pudding’ model of the atom – that negative electrons were spread throughout a positive sphere</li>
</ol>

<img src="/img/notes/02/Plum_pudding_model.svg-300x300.png" alt="Radioactive Atoms, figure 2" /></a>

<ol>
 <li>In 1911 the gold foil experiment discovered the existence of a nucleus and that most of the atom is empty space. This led to the nuclear model of the atom – Atoms have a nucleus with orbiting electrons</li>
 <li>In 1932 this was further modified to define protons and neutrons within the nucleus.</li>
</ol>

You are not expected to remember these dates or details. You do need to be familiar with the fact that the model of the atom has been developed over time in response to experimental results.

<h2 id="alpha">Alpha</h2>

Alpha radiation is made up of 2 protons and 2 neutrons (Helium Nucleus).

<img src="/img/notes/02/alpha.png" alt="Radioactive Atoms, figure 1" /></a>

When alpha radiation is released from a nucleus, the remaining nucleus will be smaller.

<img src="/img/notes/02/alpha-decay-300x218.png" alt="Radioactive Atoms, figure 2" /></a>

Alpha Decay Equation

Alpha decay can be represented using an equation

<img src="/img/notes/02/a-decay-1.png" alt="Radioactive Atoms, figure 3" /></a>

To work out what element is left after the decay:

<ol>
 <li>Balance mass numbers on each side of the equation</li>
 <li>Balance atomic numbers on each side of the equation</li>
 <li>Look up ‘daughter’ element in periodic table __using atomic number __(NOT mass number as isotopes can have different mass numbers)</li>
</ol>

<img src="/img/notes/02/a-decay-2-300x88.png" alt="Radioactive Atoms, figure 4" /></a>

<h2 id="beta">Beta</h2>

With Beta decay, a neutron decays into a proton and an electron. The proton remains in the nucleus and the electron is released. (Beta radiation is an electron)

<img src="/img/notes/02/beta.png" alt="Radioactive Atoms, figure 1" /></a>

The remaining nucleus will have the same mass but will have one more proton and one less neutron.

<img src="/img/notes/02/beta-decay-300x199.png" alt="Radioactive Atoms, figure 2" /></a>

Beta Decay Equation

Beta decay can also be represented using an equation:

<img src="/img/notes/02/b-decay-1.png" alt="Radioactive Atoms, figure 3" /></a>

<ol>
 <li>Balance mass numbers on each side of the equation</li>
 <li>Balance atomic numbers on each side of the equation (one extra proton in ‘daughter’ element)</li>
 <li>Look up ‘daughter’ element in periodic table __using atomic number __(NOT mass number as isotopes can have different mass numbers)</li>
</ol>

<img src="/img/notes/02/b-decay-2-300x95.png" alt="Radioactive Atoms, figure 4" /></a>

<h2 id="gamma">Gamma</h2>

Gamma is an electromagnetic wave. As it is not a particle, it has no mass.

It does not affect the number of particles or mass of the nucleus, so there is no decay equation for gamma radiation.

<dl>
	<dt>How many neutrons are in the nucleus of an atom of Oxygen-16?</dt>
	<dd id="Gamma0" class="js-click-to-reveal">8</dd>
	<dt>How many neutrons are in the nucleus of an atom of Oxygen-14?</dt>
	<dd id="Gamma1" class="js-click-to-reveal">6</dd>
	<dt>If Potassium-40 decays by emitting beta radiation, what is the mass number of the remaining isotope?</dt>
	<dd id="Gamma2" class="js-click-to-reveal">40</dd>
	<dt>If Uranium-235 decays by emitting alpha radiation, what is the mass number of the remaining isotope? </dt>
	<dd id="Gamma3" class="js-click-to-reveal">231</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Radioactive Atoms</h1>
</header>

<main class="blog-post__content">
	<h2 id="rutherford-geiger-marsden-gold-foil-experiment">Rutherford-Geiger-Marsden (Gold Foil) Experiment</h2>

	In this experiment, positively charged alpha particles were directed at a gold foil with a fluorescent screen to detect the alpha particles after they interacted with the foil.

	<a href="/img/notes/02/Geiger-Marsden_experiment.svg-300x195.png" target="_blank"><img src="/img/notes/02/Geiger-Marsden_experiment.svg-300x195.png" alt="Radioactive Atoms, figure 1" /></a>

	Most of the alpha particles passed straight through the foil, with others passing through on a deflected path and a smaller amount bouncing back off the foil.

	This led to a number of conclusions:

	<ol>
		<li>Most of the atom is empty space (because most alpha particles passed through)</li>
		<li>Most of the mass is concentrated in a small space (nucleus)</li>
		<li>The nucleus has a positive charge (because it repelled the positive alpha particles)</li>
		<li>The nucleus is surrounded by orbiting electrons</li>
	</ol>

	<a href="/img/notes/02/rutherford-300x263.png" target="_blank"><img src="/img/notes/02/rutherford-300x263.png" alt="Radioactive Atoms, figure 2" /></a>

	<h2 id="scientific-method">Scientific Method</h2>

	The scientific method describes how theories are developed and modified:

	<ol>
		<li>Evidence is collected from an experiment</li>
		<li>A theory is developed to explain the evidence</li>
		<li>The theory is tested with further investigations/results</li>
		<li>The theory is modified if necessary based on the further evidence</li>
	</ol>

	You use this process regularly without realizing it! For example:

	<ol>
		<li>The light bulb does not come on when you press the switch (evidence)</li>
		<li>The bulb might be broken (theory)</li>
		<li>Replace the bulb and try again (testing theory)</li>
		<li>If the new bulb works, your theory was proved to be correct</li>
		<li>If the new bulb does not work, your theory needs to be modified (e.g., there may be a problem with the wiring)</li>
	</ol>

	<h2 id="isotopes">Isotopes</h2>

	The atomic number for an element is the number of protons in the nucleus of that element. This does not change for a particular element. If there is a different number of protons, it is a different element.

	The mass number is the number of particles in the nucleus (protons and neutrons) for an element. The mass number for a particular element can vary as the number of neutrons can be different (still the same element).

	<a href="/img/notes/02/1-2-300x150.png" target="_blank"><img src="/img/notes/02/1-2-300x150.png" alt="Radioactive Atoms, figure 1" /></a>

	Isotopes have the same number of protons as the original element but different numbers of neutrons.

	Some isotopes are unstable/radioactive. These unstable isotopes will decay, emitting radiation from the nucleus.

	Hydrogen

	For example, most hydrogen atoms have 1 proton and 1 electron:

	<a href="/img/notes/02/hydrogen-isotopes.png" target="_blank"><img class="img-30" src="/img/notes/02/hydrogen-isotopes.png" alt="Radioactive Atoms, figure 2" /></a>

	But two other isotopes of hydrogen also exist:

	Deuterium (1 proton and 1 neutron)

	Tritium (1 proton and 2 neutrons)

	Carbon

	<a href="/img/notes/02/carbon-isotopes.png" target="_blank"><img class="img-20" src="/img/notes/02/carbon-isotopes.png" alt="Radioactive Atoms, figure 3" /></a>

	Most Carbon exists as Carbon-12 (6 protons &amp; 6 neutrons)

	Carbon-11 is an isotope of carbon that has 6 protons (because carbon always has 6 protons) and 5 neutrons (because the mass number is 11)

	Other isotopes of carbon also exist. Some isotopes are unstable (radioactive).

	For isotopes:

	<ol>
		<li>Mass number is different</li>
		<li>Atomic number is the same</li>
	</ol>

	<h2 id="radioactive-decay">Radioactive Decay</h2>

	When an unstable isotope decays, it releases radiation from the nucleus. The remaining nucleus will have different numbers of particles.

	There are three types of radiation – alpha, beta, and gamma:

	<a href="/img/notes/02/types-of-radiation.png" target="_blank"><img src="/img/notes/02/types-of-radiation.png" alt="Radioactive Atoms, figure 1" /></a>

	<h2 id="developing-the-model-of-the-atom">Developing the Model of the Atom</h2>

	<a href="/img/notes/02/sphere-300x300.png" target="_blank"><img class="img-20" src="/img/notes/02/sphere-300x300.png" alt="Radioactive Atoms, figure 1" /></a>

	<ol>
		<li>The Greek philosopher Democritus named the smallest (indivisible) parts of a substance 'atoms'</li>
		<li>In 1897, electrons were discovered. This led to the 'plum pudding' model of the atom – that negative electrons were spread throughout a positive sphere</li>
	</ol>

	<a href="/img/notes/02/Plum_pudding_model.svg-300x300.png" target="_blank"><img class="img-20" src="/img/notes/02/Plum_pudding_model.svg-300x300.png" alt="Radioactive Atoms, figure 2" /></a>

	<ol>
		<li>In 1911, the gold foil experiment discovered the existence of a nucleus and that most of the atom is empty space. This led to the nuclear model of the atom – Atoms have a nucleus with orbiting electrons</li>
		<li>In 1932, this was further modified to define protons and neutrons within the nucleus.</li>
	</ol>

	You are not expected to remember these dates or details. You do need to be familiar with the fact that the model of the atom has been developed over time in response to experimental results.

	<h2 id="alpha">Alpha</h2>

	Alpha radiation is made up of 2 protons and 2 neutrons (Helium Nucleus).

	<a href="/img/notes/02/alpha.png" target="_blank"><img class="img-30" src="/img/notes/02/alpha.png" alt="Radioactive Atoms, figure 1" /></a>

	When alpha radiation is released from a nucleus, the remaining nucleus will be smaller.

	<a href="/img/notes/02/alpha-decay-300x218.png" target="_blank"><img class="img-30" src="/img/notes/02/alpha-decay-300x218.png" alt="Radioactive Atoms, figure 2" /></a>

	Alpha Decay Equation

	Alpha decay can be represented using an equation

	<a href="/img/notes/02/a-decay-1.png" target="_blank"><img<header>
	<h1 class="blog-post__title">Radioactive Atoms</h1>
</header>

<main class="blog-post__content">
	<h2 id="rutherford-geiger-marsden-gold-foil-experiment">Rutherford-Geiger-Marsden (Gold Foil) Experiment</h2>

	In this experiment, positively charged alpha particles were directed at a gold foil with a fluorescent screen to detect the alpha particles after they interacted with the foil.

	<a href="/img/notes/02/Geiger-Marsden_experiment.svg-300x195.png" target="_blank"><img src="/img/notes/02/Geiger-Marsden_experiment.svg-300x195.png" alt="Radioactive Atoms, figure 1" /></a>

	Most of the alpha particles passed straight through the foil, with others passing through on a deflected path and a smaller amount bouncing back off the foil.

	This led to a number of conclusions:

	<ol>
		<li>Most of the atom is empty space (because most alpha particles passed through)</li>
		<li>Most of the mass is concentrated in a small space (nucleus)</li>
		<li>The nucleus has a positive charge (because it repelled the positive alpha particles)</li>
		<li>The nucleus is surrounded by orbiting electrons</li>
	</ol>

	<a href="/img/notes/02/rutherford-300x263.png" target="_blank"><img src="/img/notes/02/rutherford-300x263.png" alt="Radioactive Atoms, figure 2" /></a>

	<h2 id="scientific-method">Scientific Method</h2>

	The scientific method describes how theories are developed and modified:

	<ol>
		<li>Evidence is collected from an experiment</li>
		<li>A theory is developed to explain the evidence</li>
		<li>The theory is tested with further investigations/results</li>
		<li>The theory is modified if necessary based on the further evidence</li>
	</ol>

	You use this process regularly without realizing it! For example:

	<ol>
		<li>The light bulb does not come on when you press the switch (evidence)</li>
		<li>The bulb might be broken (theory)</li>
		<li>Replace the bulb and try again (testing theory)</li>
		<li>If the new bulb works, your theory was proved to be correct</li>
		<li>If the new bulb does not work, your theory needs to be modified (e.g., there may be a problem with the wiring)</li>
	</ol>

	<h2 id="isotopes">Isotopes</h2>

	The atomic number for an element is the number of protons in the nucleus of that element. This does not change for a particular element. If there is a different number of protons, it is a different element.

	The mass number is the number of particles in the nucleus (protons and neutrons) for an element. The mass number for a particular element can vary as the number of neutrons can be different (still the same element).

	<a href="/img/notes/02/1-2-300x150.png" target="_blank"><img src="/img/notes/02/1-2-300x150.png" alt="Radioactive Atoms, figure 1" /></a>

	Isotopes have the same number of protons as the original element but different numbers of neutrons.

	Some isotopes are unstable/radioactive. These unstable isotopes will decay, emitting radiation from the nucleus.

	Hydrogen

	For example, most hydrogen atoms have 1 proton and 1 electron:

	<a href="/img/notes/02/hydrogen-isotopes.png" target="_blank"><img class="img-30" src="/img/notes/02/hydrogen-isotopes.png" alt="Radioactive Atoms, figure 2" /></a>

	But two other isotopes of hydrogen also exist:

	Deuterium (1 proton and 1 neutron)

	Tritium (1 proton and 2 neutrons)

	Carbon

	<a href="/img/notes/02/carbon-isotopes.png" target="_blank"><img class="img-20" src="/img/notes/02/carbon-isotopes.png" alt="Radioactive Atoms, figure 3" /></a>

	Most Carbon exists as Carbon-12 (6 protons &amp; 6 neutrons)

	Carbon-11 is an isotope of carbon that has 6 protons (because carbon always has 6 protons) and 5 neutrons (because the mass number is 11)

	Other isotopes of carbon also exist. Some isotopes are unstable (radioactive).

	For isotopes:

	<ol>
		<li>Mass number is different</li>
		<li>Atomic number is the same</li>
	</ol>

	<h2 id="radioactive-decay">Radioactive Decay</h2>

	When an unstable isotope decays, it releases radiation from the nucleus. The remaining nucleus will have different numbers of particles.

	There are three types of radiation – alpha, beta, and gamma:

	<a href="/img/notes/02/types-of-radiation.png" target="_blank"><img src="/img/notes/02/types-of-radiation.png" alt="Radioactive Atoms, figure 1" /></a>

	<h2 id="developing-the-model-of-the-atom">Developing the Model of the Atom</h2>

	<a href="/img/notes/02/sphere-300x300.png" target="_blank"><img class="img-20" src="/img/notes/02/sphere-300x300.png" alt="Radioactive Atoms, figure 1" /></a>

	<ol>
		<li>The Greek philosopher Democritus named the smallest (indivisible) parts of a substance 'atoms'</li>
		<li>In 1897, electrons were discovered. This led to the 'plum pudding' model of the atom – that negative electrons were spread throughout a positive sphere</li>
	</ol>

	<a href="/img/notes/02/Plum_pudding_model.svg-300x300.png" target="_blank"><img class="img-20" src="/img/notes/02/Plum_pudding_model.svg-300x300.png" alt="Radioactive Atoms, figure 2" /></a>

	<ol>
		<li>In 1911, the gold foil experiment discovered the existence of a nucleus and that most of the atom is empty space. This led to the nuclear model of the atom – Atoms have a nucleus with orbiting electrons</li>
		<li>In 1932, this was further modified to define protons and neutrons within the nucleus.</li>
	</ol>

	You are not expected to remember these dates or details. You do need to be familiar with the fact that the model of the atom has been developed over time in response to experimental results.

	<h2 id="alpha">Alpha</h2>

	Alpha radiation is made up of 2 protons and 2 neutrons (Helium Nucleus).

	<a href="/img/notes/02/alpha.png" target="_blank"><img class="img-30" src="/img/notes/02/alpha.png" alt="Radioactive Atoms, figure 1" /></a>

	When alpha radiation is released from a nucleus, the remaining nucleus will be smaller.

	<a href="/img/notes/02/alpha-decay-300x218.png" target="_blank"><img class="img-30" src="/img/notes/02/alpha-decay-300x218.png" alt="Radioactive Atoms, figure 2" /></a>

	Alpha Decay Equation

	Alpha decay can be represented using an equation

	<a href="/img/notes/02/a-decay-1.png" target="_blank"><img class="img-30" src="/img/notes/02/a-decay-1.png" alt="Radioactive Atoms, figure 3" /></a>

	To work out what element is left after the decay:

	<ol>
		<li>Balance mass numbers on each side of the equation</li>
		<li>Balance atomic numbers on each side of the equation</li>
		<li>Look up 'daughter' element in the periodic table using atomic number (NOT mass number as isotopes can have different mass numbers)</li>
	</ol>

	<a href="/img/notes/02/a-decay-2-300x88.png" target="_blank"><img class="img-30" src="/img/notes/02/a-decay-2-300x88.png" alt="Radioactive Atoms, figure 4" /></a>

	<h2 id="beta">Beta</h2>

	With Beta decay, a neutron decays into a proton and an electron. The proton remains in the nucleus, and the electron is released. (Beta radiation is an electron)

	<a href="/img/notes/02/beta.png" target="_blank"><img class="img-30" src="/img/notes/02/beta.png" alt="Radioactive Atoms, figure 1" /></a>

	The remaining nucleus will have the same mass but will have one more proton and one less neutron.

	<a href="/img/notes/02/beta-decay-300x199.png" target="_blank"><img class="img-30" src="/img/notes/02/beta-decay-300x199.png" alt="Radioactive Atoms, figure 2" /></a>

	Beta Decay Equation

	Beta decay can also be represented using an equation:

	<a href="/img/notes/02/b-decay-1.png" target="_blank"><img class="img-30" src="/img/notes/02/b-decay-1.png" alt="Radioactive Atoms, figure 3" /></a>

	<ol>
		<li>Balance mass numbers on each side of the equation</li>
		<li>Balance atomic numbers on each side of the equation (one extra proton in 'daughter' element)</li>
		<li>Look up 'daughter' element in the periodic table using atomic number (NOT mass number as isotopes can have different mass numbers)</li>
	</ol>

	<a href="/img/notes/02/b-decay-2-300x95.png" target="_blank"><img class="img-30" src="/img/notes/02/b-decay-2-300x95.png" alt="Radioactive Atoms, figure 4" /></a>

	<h2 id="gamma">Gamma</h2>

	Gamma is an electromagnetic wave. As it is not a particle, it has no mass.

	It does not affect the number of particles or mass of the nucleus, so there is no decay equation for gamma radiation.

	<dl>
		<dt>How many neutrons are in the nucleus of an atom of Oxygen-16?</dt>
		<dd id="Gamma0" class="js-click-to-reveal">8</dd>
		<dt>How many neutrons are in the nucleus of an atom of Oxygen-14?</dt>
		<dd id="Gamma1" class="js-click-to-reveal">6</dd>
		<dt>If Potassium-40 decays by emitting beta radiation, what is the mass number of the remaining isotope?</dt>
		<dd id="Gamma2" class="js-click-to-reveal">40</dd>
		<dt>If Uranium-235 decays by emitting alpha radiation, what is the mass number of the remaining isotope? </dt>
		<dd id="Gamma3" class="js-click-to-reveal">231</dd>
	</dl>


</main>

Radioactive Atoms

Atomic Structure

<header>
			<h1 class="blog-post__title">Properties of Radiation</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="range">Range</h2>

Alpha can travel a few centimetres in air.

Beta can travel a few metres.

Gamma rays have an almost infinite range.

<img src="/img/notes/02/range.png" alt="Properties of Radiation, figure 1" /></a>

<h2 id="penetration">Penetration</h2>

Alpha can be absorbed by paper or skin.

Beta can be absorbed by thin aluminium.

Gamma rays can be absorbed by thick lead.

<img src="/img/notes/02/penetration.png" alt="Properties of Radiation, figure 1" /></a>

<h2 id="magnetic-and-electric-fields">Magnetic and Electric Fields</h2>

Gamma rays will pass through a field unaffected as they have no charge and no mass.

Beta will be deflected towards the positive area of the field. It has a low mass so will be strongly deflected.

Alpha will be deflected towards the negative area of the field. It has a high mass so will be weakly deflected.

<img src="/img/notes/02/field.png" alt="Properties of Radiation, figure 1" /></a>

###

<h2 id="danger">Danger</h2>

Which type of radiation is the most dangerous depends on the situation. Alpha is the most ionising but is least likely to reach you due to it’s short range and low penetration. Gamma is the least ionising but is the most likely to reach you due to it’s long range and high penetration.

You can be exposed to radiation in two ways:

<ol>
 <li>Irradiation: Exposure to a radioactive source outside of your body</li>
 <li>Contamination: Exposure to a radioactive source inside your body</li>
</ol>

<h2 id="half-life">Half Life</h2>

The half-life is the time it takes the (radio)activity of a substance to decrease by half.

Half-life can be calculated from a graph of the activity level of a radioactive substance over time. At any point on the graph (but it’s usually easiest to do it from the start), work out the time taken for the activity to drop by half – this is the half-life.

<img src="/img/notes/02/half-life.png" alt="Properties of Radiation, figure 1" /></a>

If the half-life is 4 minutes, then every 4 minutes, the activity will decrease by half.

Half-life can also be calculated numerically.

For example:

A sample of Bismuth-214 has an activity of 64Bq. It has a half-life of 20 minutes.

<ol>
 <li>After 20mins (1 half-life), the activity will be 32Bq (half the original activity</li>
 <li>After 40mins (2 half-lives), the activity will be 16Bq (half again)</li>
 <li>After 60mins (3 half-lives) the activity will be 8Bq</li>
</ol>

And so on.

<h2 id="ionisation">Ionisation</h2>

Ionising radiation has enough energy to move electrons from atoms. This is harmful to cells in your body (cancer). Ionising radiation can also be used to kill cancerous cells.

Alpha is the most ionising.

Gamma is the least ionising.

<img src="/img/notes/02/ionisation-1.png" alt="Properties of Radiation, figure 1" /></a>

<h2 id="background-radiation">Background Radiation</h2>

Some elements emit ionising radiation all the time. These radioactive elements are naturally found in the environment. Background radiation includes natural and man-made radioactive sources.

<img src="/img/notes/02/background-radiaton-1.png" alt="Properties of Radiation, figure 1" /></a>

<img src="/img/notes/02/background-radiaton-2.png" alt="Properties of Radiation, figure 2" /></a>

<img src="/img/notes/02/radiation-exposure.png" alt="Properties of Radiation, figure 3" /></a>

Exposure to radiation can happen in two ways:

<ol>
 <li>Irradiation - Exposure to radiation from a source outside your body</li>
 <li>Contamination - Exposure to radiation from a source inside your body</li>
</ol>

<h2 id="carbon-dating">Carbon Dating</h2>

Living things contain some radioactive carbon-14. When the organism dies, it stops taking in carbon-14. The carbon-14 decays to carbon-12. The half-life of carbon-14 is 5600 years. The level of radiation emitted from the carbon 14 can be used to work out how long ago the organism died.

Worked Example

A living bone emits 170 counts per minute. A bone from an archeological site emits 50cpm. The background radiation in the area is 10 cpm. How old is the bone? (Half-life of Carbon = 5600years)

<ol>
 <li>Fresh bone – background radiation = 170 – 10 = 160cpm</li>
 <li>Ancient bone – background radiation = 50 – 10 = 40cpm</li>
 <li>Fresh = 160cpm. 1 half-life later = 80cpm. After 2 half-lives = 40cpm</li>
 <li>The ancient bone is 2 half-lives old.</li>
 <li>Half-life = 5600 years</li>
</ol>

Ancient bone = 120,000 years old

<h2 id="safety-precautions">Safety Precautions</h2>

The risk to general public from radioactive materials is low, but people working with radioactive substances need to take precautions.

They can avoid contamination by:

<ol>
 <li>Careful storage of radioactive materials</li>
 <li>Wearing gloves/protective clothing</li>
</ol>

They can reduce irradiation by:

<ol>
 <li>Working behind lead shields/barriers</li>
 <li>Reducing time in at risk areas</li>
</ol>

Monitor exposure using a film badge

<h2 id="using-radiation">Using Radiation</h2>

When using radioactive materials, the properties of the source need to be matched to the specific need of that task considering:

<ol>
 <li>Range</li>
 <li>Penetration</li>
 <li>Ionisation</li>
 <li>Half-life</li>
</ol>

Medical Diagnosis - Gamma Camera

<img src="/img/notes/02/gamma-camera.png" alt="Properties of Radiation, figure 1" /></a>

To use a scan from a gamma camera, the patient swallows a gamma tracer or has it injected into the bloodstream. The camera detects the gamma radiation emitted from the body, producing an image of the body parts containing the tracer.

A gamma source is used as it is the least ionising and will pass through the body easily to be detected by the camera. It is important to choose a half-life which is long enough to allow the scan to be carried out but not so long that the patient remains contaminated for a long time.

Medical Treatment – Radiotherapy

<img src="/img/notes/02/radiotherapy-1024x681.jpg" alt="Properties of Radiation, figure 2" /></a>

As ionising radiation is dangerous to cells, it can be used to kill cancerous cells. The radiation is targeted at the tumour, but some damage to healthy cells is inevitable. Gamma or beta sources are usually used as alpha cannot penetrate the skin.

Sterilisation

<img src="/img/notes/02/sterilisation.jpg" alt="Properties of Radiation, figure 3" /></a>

Radiation can be used to kill bacteria and therefore sterilise surgical equipment. The items can be sealed in air-tight packaging before being irradiated, which means there is no chance of re-contamination before they are used.

Measuring Thickness

<img src="/img/notes/02/thickness.png" alt="Properties of Radiation, figure 4" /></a>

Radioactive sources can be used to measure the thickness of materials that are being rolled out, such as paper or sheet metal. The source is positioned on one side of the material with a detector on the other side. A change in thickness will affect the amount of radiation passing through the material and being received by the detector. This can be used to change the pressure of the rollers to increase/decrease the thickness as necessary.

Beta is used for paper (as alpha can not pass through paper and gamma would pass through too easily). Gamma is used for metal as alpha and beta can not pass through.

Smoke Detectors

<img src="/img/notes/02/smoke-alarm.png" alt="Properties of Radiation, figure 5" /></a>

Smoke detectors use an alpha source which ionises the air in a small gap in a circuit, allowing current to flow.

If smoke is present, it absorbs the alpha radiation meaning current can now no longer flow across the gap, this triggers the alarm.

An alpha source is used because it can not penetrate through smoke. Beta and Gamm would not be suitable as they can pass through smoke.

<dl>
	<dt>Which type of radiation is the most ionising?</dt>
	<dd id="Using-Radiation0" class="js-click-to-reveal">alpha</dd>
	<dt>Which type of radiation has no electrical charge?</dt>
	<dd id="Using-Radiation1" class="js-click-to-reveal">gamma</dd>
	<dt>Which type of radiation has the largest range?</dt>
	<dd id="Using-Radiation2" class="js-click-to-reveal">gamma</dd>
	<dt>The activity of a radioactive sample is 1440Bq. 5 hours later it is 45Bq. What is the half life of this sample?</dt>
	<dd id="Using-Radiation3" class="js-click-to-reveal">Your answer should include: 1 hour / 1</dd>
	<dt>The half life of Strontium-90 is 29 years. If you start with 1000 nuclei of Strontium-90, how many would you expect to be left after 87 years?</dt>
	<dd id="Using-Radiation4" class="js-click-to-reveal">125</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Properties of Radiation</h1>
</header>

<main class="blog-post__content">
	<h2 id="range">Range</h2>

	Alpha particles can travel a few centimeters in air.

	Beta particles can travel a few meters.

	Gamma rays have an almost infinite range.

	<a href="/img/notes/02/range.png" target="_blank"><img src="/img/notes/02/range.png" alt="Properties of Radiation, figure 1" /></a>

	<h2 id="penetration">Penetration</h2>

	Alpha particles can be absorbed by paper or skin.

	Beta particles can be absorbed by thin aluminum.

	Gamma rays can be absorbed by thick lead.

	<a href="/img/notes/02/penetration.png" target="_blank"><img src="/img/notes/02/penetration.png" alt="Properties of Radiation, figure 1" /></a>

	<h2 id="magnetic-and-electric-fields">Magnetic and Electric Fields</h2>

	Gamma rays will pass through a field unaffected as they have no charge and no mass.

	Beta particles will be deflected towards the positive area of the field. They have a low mass, so they will be strongly deflected.

	Alpha particles will be deflected towards the negative area of the field. They have a high mass, so they will be weakly deflected.

	<a href="/img/notes/02/field.png" target="_blank"><img src="/img/notes/02/field.png" alt="Properties of Radiation, figure 1" /></a>

	<h2 id="danger">Danger</h2>

	Which type of radiation is the most dangerous depends on the situation. Alpha particles are the most ionizing but are least likely to reach you due to their short range and low penetration. Gamma rays are the least ionizing but are the most likely to reach you due to their long range and high penetration.

	You can be exposed to radiation in two ways:

	<ol>
		<li>Irradiation: Exposure to a radioactive source outside of your body</li>
		<li>Contamination: Exposure to a radioactive source inside your body</li>
	</ol>

	<h2 id="half-life">Half Life</h2>

	The half-life is the time it takes for the (radio)activity of a substance to decrease by half.

	Half-life can be calculated from a graph of the activity level of a radioactive substance over time. At any point on the graph (but it’s usually easiest to do it from the start), work out the time taken for the activity to drop by half – this is the half-life.

	<a href="/img/notes/02/half-life.png" target="_blank"><img src="/img/notes/02/half-life.png" alt="Properties of Radiation, figure 1" /></a>

	If the half-life is 4 minutes, then every 4 minutes, the activity will decrease by half.

	Half-life can also be calculated numerically.

	For example:

	A sample of Bismuth-214 has an activity of 64 Bq. It has a half-life of 20 minutes.

	<ol>
		<li>After 20 minutes (1 half-life), the activity will be 32 Bq (half the original activity).</li>
		<li>After 40 minutes (2 half-lives), the activity will be 16 Bq (half again).</li>
		<li>After 60 minutes (3 half-lives), the activity will be 8 Bq.</li>
	</ol>

	And so on.

	<h2 id="ionisation">Ionisation</h2>

	Ionizing radiation has enough energy to move electrons from atoms. This is harmful to cells in your body and can cause cancer. Ionizing radiation can also be used to kill cancerous cells.

	Alpha particles are the most ionizing.

	Gamma rays are the least ionizing.

	<a href="/img/notes/02/ionisation-1.png" target="_blank"><img src="/img/notes/02/ionisation-1.png" alt="Properties of Radiation, figure 1" /></a>

	<h2 id="background-radiation">Background Radiation</h2>

	Some elements emit ionizing radiation all the time. These radioactive elements are naturally found in the environment. Background radiation includes natural and man-made radioactive sources.

	<a href="/img/notes/02/background-radiation-1.png" target="_blank"><img src="/img/notes/02/background-radiation-1.png" alt="Properties of Radiation, figure 1" /></a>

	<a href="/img/notes/02/background-radiation-2.png" target="_blank"><img src="/img/notes/02/background-radiation-2.png" alt="Properties of Radiation, figure 2" /></a>

	<a href="/img/notes/02/radiation-exposure.png" target="_blank"><img src="/img/notes/02/radiation-exposure.png" alt="Properties of Radiation, figure 3" /></a>

	Exposure to radiation can happen in two ways:

	<ol>
		<li>Irradiation - Exposure to radiation from a source outside your body</li>
		<li>Contamination - Exposure to radiation from a source inside your body</li>
	</ol>

	<h2 id="carbon-dating">Carbon Dating</h2>

	Living things contain some radioactive carbon-14. When the organism dies, it stops taking in carbon-14. The carbon-14 decays to carbon-12. The half-life of carbon-14 is 5600 years. The level of radiation emitted from the carbon-14 can be used to work out how long ago the organism died.

	Worked Example:

	A living bone emits 170 counts per minute. A bone from an archaeological site emits 50 cpm. The background radiation in the area is 10 cpm. How old is the bone? (Half-life of Carbon = 5600 years)

	<ol>
		<li>Fresh bone – background radiation = 170 – 10 = 160 cpm</li>
		<li>Ancient bone – background radiation = 50 – 10 = 40 cpm</li>
		<li>Fresh = 160 cpm. 1 half-life later = 80 cpm. After 2 half-lives = 40 cpm</li>
		<li>The ancient bone is 2 half-lives old.</li>
		<li>Half-life = 5600 years</li>
	</ol>

	Ancient bone = 120,000 years old

	<h2 id="safety-precautions">Safety Precautions</h2>

	The risk to the general public from radioactive materials is low, but people working with radioactive substances need to take precautions.

	They can avoid contamination by:

	<ol>
		<li>Careful storage of radioactive materials</li>
		<li>Wearing gloves/protective clothing</li>
	</ol>

	They can reduce irradiation by:

	<ol>
		<li>Working behind lead shields/barriers</li>
		<li>Reducing time in at-risk areas</li>
	</ol>

	Monitor exposure using a film badge.

	<h2 id="using-radiation">Using Radiation</h2>

	When using radioactive materials, the properties of the source need to be matched to the specific need of that task considering:

	<ol>
		<li>Range</li>
		<li>Penetration</li>
		<li>Ionisation</li>
		<li>Half-life</li>
	</ol>

	Medical Diagnosis - Gamma Camera

	<a href="/img/notes/02/gamma-camera.png" target="_blank"><img src="/img/notes/02/gamma-camera.png" alt="Properties of Radiation, figure 1" /></a>

	To use a scan from a gamma camera, the patient swallows a gamma tracer or has it injected into the bloodstream. The camera detects the gamma radiation emitted from the body, producing an image of the body parts containing the tracer.

	A gamma source is used as it is the least ionizing and will pass through the body easily to be detected by the camera. It is important to choose a half-life that is long enough to allow the scan to be carried out but not so long that the patient remains contaminated for a long time.

	Medical Treatment – Radiotherapy

	<a href="/img/notes/02/radiotherapy-1024x681.jpg" target="_blank"><img src="/img/notes/02/radiotherapy-1024x681.jpg" alt="Properties of Radiation, figure 2" /></a>

	As ionizing radiation is dangerous to cells, it can be used to kill cancerous cells. The radiation is targeted at the tumor, but some damage to healthy cells is inevitable. Gamma or beta sources are usually used as alpha particles cannot penetrate the skin.

	Sterilization

	<a href="/img/notes/02/sterilization.jpg" target="_blank"><img src="/img/notes/02/sterilization.jpg" alt="Properties of Radiation, figure 3" /></a>

	Radiation can be used to kill bacteria and therefore sterilize surgical equipment. The items can be sealed in airtight packaging before being irradiated, which means there is no chance of re-contamination before they are used.

	Measuring Thickness

	<a href="/img/notes/02/thickness.png" target="_blank"><img src="/img/notes/02/thickness.png" alt="Properties of Radiation, figure 4" /></a>

	Radioactive sources can be used to measure the thickness of materials that are being rolled out, such as paper or sheet metal. The source is positioned on one side of the material with a detector on the other side. A change in thickness will affect the amount of radiation passing through the material and being received by the detector. This can be used to change the pressure of the rollers to increase/decrease the thickness as necessary.

	Beta particles are used for paper (as alpha particles cannot pass through paper and gamma rays would pass through too easily). Gamma rays are used for metal as alpha and beta particles cannot pass through.

	Smoke Detectors

	<a href="/img/notes/02/smoke-alarm.png" target="_blank"><img src="/img/notes/02/smoke-alarm.png" alt="Properties of Radiation, figure 5" /></a>

	Smoke detectors use an alpha source, which ionizes the air in a small gap in a circuit, allowing current to flow.

	If smoke is present, it absorbs the alpha radiation, meaning current can no longer flow across the gap, triggering the alarm.

	An alpha source is used because it cannot penetrate through smoke. Beta and gamma rays would not be suitable as they can pass through smoke.

	<dl>
		<dt>Which type of radiation is the most ionizing?</dt>
		<dd id="Using-Radiation0" class="js-click-to-reveal">Alpha</dd>
		<dt>Which type of radiation has no electrical charge?</dt>
		<dd id="Using-Radiation1" class="js-click-to-reveal">Gamma</dd>
		<dt>Which type of radiation has the largest range?</dt>
		<dd id="Using-Radiation2" class="js-click-to-reveal">Gamma</dd>
		<dt>The activity of a radioactive sample is 1440 Bq. 5 hours later it is 45 Bq. What is the half-life of this sample?</dt>
		<dd id="Using-Radiation3" class="js-click-to-reveal">Your answer should include: 1 hour / 1</dd>
		<dt>The half-life of Strontium-90 is 29 years. If you start with 1000 nuclei of Strontium-90, how many would you expect to be left after 87 years?</dt>
		<dd id="Using-Radiation4" class="js-click-to-reveal">125</dd>
	</dl>
</main>

Properties of Radiation

<header>
			<h1 class="blog-post__title">Fusion and Fission</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="nuclear-fission">Nuclear Fission</h2>

Nuclear fission is splitting a nucleus, this releases energy. The energy can be used to heat water and produce steam in a nuclear power station.

There are two commonly used radioactive substances in power stations:

<ol>
 <li>Uranium-235</li>
 <li>Plutonium-239</li>
</ol>

<img src="/img/notes/02/fission-gif.gif" alt="Fusion and Fission, figure 1" /></a>

A neutron is targeted at the radioactive nucleus. The nucleus splits into two smaller nuclei and more neutrons are released. This can start a chain reaction

<img src="/img/notes/02/chain-reaction.png" alt="Fusion and Fission, figure 2" /></a>

The explosion caused by a nuclear weapon is caused by an uncontrolled chain reaction

<img src="/img/notes/02/nuclear-weapon.jpg" alt="Fusion and Fission, figure 3" /></a>

The chain reaction is controlled in a reactor to control the amount of energy released

<img src="/img/notes/02/control-rods.png" alt="Fusion and Fission, figure 4" /></a>

<ol>
 <li>Control rods can absorb neutrons</li>
 <li>Raising or lowering the control rods can increase or decrease the rate of the chain reaction</li>
</ol>

Advantages of Nuclear (fission) power stations:

<ol>
 <li>Only small amounts of fuel needed (not in danger of running out)</li>
 <li>Low running costs</li>
 <li>No gas emissions</li>
 <li>High power output</li>
</ol>

Disadvantages of Nuclear (fission) power stations:

<ol>
 <li>Radioactive waste produced</li>
 <li>High, intermediate and low level waste</li>
 <li>Emits ionising radiation – harmful to humans</li>
 <li>Radioactive for a long time</li>
 <li>Storage needs to be secure and permanent</li>
 <li>Power stations are expensive to build and decommission (dismantle)</li>
 <li>Safety – accidents are rare but, if they do happen, they can be catastrophic (see Chernobyl</a>)</li>
</ol>

<h2 id="nuclear-fusion">Nuclear Fusion</h2>

In the nucleus of an atom, electromagnetic forces act between protons to repel each other. The strong nuclear force holds them together. The strong nuclear force is stronger than the electromagnetic force but only acts over very small distances.

Nuclear fusion is the joining together of two (hydrogen) nuclei. Pushing the nuclei together is difficult due to the electromagnetic repulsion between the positive charges. Once they are close enough for the strong nuclear force to act, the nuclei fuse together. A large amount of energy is released.

<img src="/img/notes/02/fusion-gif.gif" alt="Fusion and Fission, figure 1" /></a>

Fusion reactors are a source of ongoing research

Potential advantages:

<ol>
 <li>Fuel easily available (hydrogen isotopes in seawater)</li>
 <li>The waste product, Helium, is not radioactive</li>
 <li>Large amounts of energy could be produced</li>
</ol>

Current difficulties:

<ol>
 <li>Very high temperature and pressure required to overcome electrostatic repulsion</li>
 <li>This currently requires more energy than it produces!</li>
</ol>

<dl>
	<dt>Splitting a nucleus is known as nuclear ________?</dt>
	<dd id="Nuclear-Fusion0" class="js-click-to-reveal">fission</dd>
	<dt>Joining two nuclei together is known as nuclear _________?</dt>
	<dd id="Nuclear-Fusion1" class="js-click-to-reveal">fusion</dd>
	<dt>What is the name of the force that holds the particles in the nucleus together?</dt>
	<dd id="Nuclear-Fusion2" class="js-click-to-reveal">Your answer should include: strong / nuclear / force</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Fusion and Fission</h1>
</header>

<main class="blog-post__content">
	<h2 id="nuclear-fission">Nuclear Fission</h2>

	Nuclear fission involves splitting a nucleus, which releases energy that can be used to heat water and produce steam in a nuclear power station.

	There are two commonly used radioactive substances in power stations:

	<ol>
		<li>Uranium-235</li>
		<li>Plutonium-239</li>
	</ol>

	<a href="/img/notes/02/fission-gif.gif" target="_blank"><img src="/img/notes/02/fission-gif.gif" alt="Fusion and Fission, figure 1" /></a>

	A neutron is targeted at the radioactive nucleus. The nucleus splits into two smaller nuclei and more neutrons are released. This can start a chain reaction.

	<a href="/img/notes/02/chain-reaction.png" target="_blank"><img src="/img/notes/02/chain-reaction.png" alt="Fusion and Fission, figure 2" /></a>

	The explosion caused by a nuclear weapon is caused by an uncontrolled chain reaction.

	<a href="/img/notes/02/nuclear-weapon.jpg" target="_blank"><img src="/img/notes/02/nuclear-weapon.jpg" alt="Fusion and Fission, figure 3" /></a>

	The chain reaction is controlled in a reactor to control the amount of energy released.

	<a href="/img/notes/02/control-rods.png" target="_blank"><img src="/img/notes/02/control-rods.png" alt="Fusion and Fission, figure 4" /></a>

	<ol>
		<li>Control rods can absorb neutrons.</li>
		<li>Raising or lowering the control rods can increase or decrease the rate of the chain reaction.</li>
	</ol>

	Advantages of Nuclear (fission) power stations:

	<ol>
		<li>Only small amounts of fuel needed (not in danger of running out).</li>
		<li>Low running costs.</li>
		<li>No gas emissions.</li>
		<li>High power output.</li>
	</ol>

	Disadvantages of Nuclear (fission) power stations:

	<ol>
		<li>Radioactive waste produced.</li>
		<li>High, intermediate, and low-level waste.</li>
		<li>Emits ionizing radiation, which is harmful to humans.</li>
		<li>Radioactive for a long time.</li>
		<li>Storage needs to be secure and permanent.</li>
		<li>Power stations are expensive to build and decommission (dismantle).</li>
		<li>Safety – accidents are rare but, if they do happen, they can be catastrophic (<a href="https://www.youtube.com/watch?v=f5ptI6Pi3GA" target="_blank">see Chernobyl</a>).</li>
	</ol>

	<h2 id="nuclear-fusion">Nuclear Fusion</h2>

	In the nucleus of an atom, electromagnetic forces act between protons to repel each other. The strong nuclear force holds them together. The strong nuclear force is stronger than the electromagnetic force but only acts over very small distances.

	Nuclear fusion is the joining together of two (hydrogen) nuclei. Pushing the nuclei together is difficult due to the electromagnetic repulsion between the positive charges. Once they are close enough for the strong nuclear force to act, the nuclei fuse together, releasing a large amount of energy.

	<a href="/img/notes/02/fusion-gif.gif" target="_blank"><img src="/img/notes/02/fusion-gif.gif" alt="Fusion and Fission, figure 1" /></a>

	Fusion reactors are a source of ongoing research.

	Potential advantages:

	<ol>
		<li>Fuel is easily available (hydrogen isotopes in seawater).</li>
		<li>The waste product, Helium, is not radioactive.</li>
		<li>Large amounts of energy could be produced.</li>
	</ol>

	Current difficulties:

	<ol>
		<li>Very high temperature and pressure are required to overcome electrostatic repulsion.</li>
		<li>This currently requires more energy than it produces!</li>
	</ol>

	<dl>
		<dt>Splitting a nucleus is known as nuclear ________?</dt>
		<dd id="Nuclear-Fusion0" class="js-click-to-reveal">fission</dd>
		<dt>Joining two nuclei together is known as nuclear _________?</dt>
		<dd id="Nuclear-Fusion1" class="js-click-to-reveal">fusion</dd>
		<dt>What is the name of the force that holds the particles in the nucleus together?</dt>
		<dd id="Nuclear-Fusion2" class="js-click-to-reveal">strong nuclear force</dd>
	</dl>
</main>

Fusion and Fission

<header>
			<h1 class="blog-post__title">Turning Forces and Pressure</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="moments">Moments</h2>

A moment is a turning force. The size of a moment can be calculated using this equation (you DO need to remember this equation for your exam):

Moment = force x distance from pivot

The moment can be increased by:

<ol>
 <li>Increasing the size of the force</li>
 <li>Increasing the distance from the pivot</li>
</ol>

Objects will balance if the clockwise moment equals the anticlockwise moment.

For an object in equilibrium (you do NOT need to remember this equation for your exam):

W1d1__ = W__2d2

W = weight (force) (N)

d = distance from pivot (m)

Worked Example

What force is needed at A to balance the beam?

<img src="/img/notes/02/moments.png" alt="Turning Forces and Pressure, figure 1" /></a>

Clockwise moment = 6 x 4 = 24Nm

Anticlockwise moment = 8 x 2 = 16Nm

For beam to balance, anticlockwise moment must be 24Nm

Moment at A must be 8Nm (16 + 8 = 24Nm)

Force A = moment ÷ distance

Force A = 8 ÷ 4 = 2N

<h2 id="centre-of-mass">Centre of Mass</h2>

Equilibrium - An object is in equilibrium when the opposing forces on it are balanced.

Centre of mass - The point on an object through which the weight of the object acts.

For a regular, symmetrical shape with its mass evenly distributed, the centre of mass will be in the middle of the object:

<img src="/img/notes/02/cm1.png" alt="Turning Forces and Pressure, figure 1" /></a>

If the mass is not evenly distributed, the centre of mass will not be in the centre of the object:

<img src="/img/notes/02/cm2.png" alt="Turning Forces and Pressure, figure 2" /></a>

An object will balance at its centre of mass.

An object will always come to rest with its centre of mass vertically below the point of suspension.

<img src="/img/notes/02/cm3.png" alt="Turning Forces and Pressure, figure 3" /></a>

An object will fall over if it’s centre of mass moves outside the area of its base:

<img src="/img/notes/02/cm4.png" alt="Turning Forces and Pressure, figure 4" /></a>

<h2 id="levers">Levers</h2>

A lever is a simple machine that uses moments (turning forces) to make a task easier.

There are two factors that can affect the lever:

<ol>
 <li>The force applied to it (effort)</li>
 <li>The distance from the pivot</li>
</ol>

There are two types of lever:

<ol>
 <li>Force multiplier - A small effort can be used to move a large load, but has to move a greater distance</li>
 <li>__Distance multiplier __- A small movement of the effort results in a large movement of the load, but a larger force has to be used</li>
</ol>

Example:

<img src="/img/notes/02/l1.png" alt="Turning Forces and Pressure, figure 1" /></a>

The applied force is further away from the pivot than the exerted force. This means the force exerted will be greater than the force that was applied

You should be able to identify the effort (input force), pivot and load (output force) are for a variety of examples of levers:

<img src="/img/notes/02/l3-289x300.png" alt="Turning Forces and Pressure, figure 2" /></a>

<img src="/img/notes/02/l2.png" alt="Turning Forces and Pressure, figure 3" /></a><img src="/img/notes/02/l5.png" alt="Turning Forces and Pressure, figure 4" /></a>

<img src="/img/notes/02/l4.png" alt="Turning Forces and Pressure, figure 5" /></a>

<img src="/img/notes/02/l6.png" alt="Turning Forces and Pressure, figure 6" /></a>

<h2 id="gears">Gears</h2>

Gears multiply the effect of a turning force

<img src="/img/notes/02/gears-gif1.gif" alt="Turning Forces and Pressure, figure 1" /></a>

Low Gear:

<ol>
 <li>Small wheel used to turn large wheel</li>
 <li>Low speed, high turning force</li>
</ol>

<img src="/img/notes/02/gears2.gif" alt="Turning Forces and Pressure, figure 2" /></a>

High Gear:

<ol>
 <li>Large wheel used to turn small wheel</li>
 <li>High Speed, low turning force</li>
</ol>

Worked Example

A gear wheel of radius 30mm is used to turn another gear wheel of radius 15mm with a force of 90N

Calculate the moment of the force on:

<ol>
 <li>The 15mm wheel</li>
 <li>The 30mm wheel</li>
</ol>

a)

Moment = force x distance from pivot

(distance from pivot = radius of gear wheel)

Moment = 90 x 15 = 1350 Nmm (or 1.35Nm)

b)

Moment = force x distance from pivot

(distance from pivot = radius of gear wheel)

Moment = 90 x 30 = 2700 Nmm (or 2.7Nm)

<h2 id="pressure-in-liquids">Pressure in Liquids</h2>

Pressure in liquids increases with depth. If a container of water has three holes in the side, the water will shoot out further from the lowest hole because the pressure is greatest at the bottom of the container.

<img src="/img/notes/02/liquid-pressure.png" alt="Turning Forces and Pressure, figure 1" /></a>

Pressure in liquids also depends on the density of the liquid. The relationship between pressure, density and depth can be shown by this equation (you do NOT need to remember this equation for the exam):

p = hρg

p = pressure (Pa)

h = height (m)

ρ = density (kg/m3) **be careful as this looks a lot like p!**

g = gravitational field strength (N/kg)

Worked Example

Calculate the pressure of sea water (density 1050 kg/m3) at a depth of 100m. (g = 9.8 N/kg)

pressure = hρg

pressure = 100 x 1050 x 9.8

pressure = 1,029,000 Pa

<h2 id="pressure">Pressure</h2>

Surface Pressure

Pressure is a force acting on an area. Pressure can be calculated using the following equation (you DO need to remember this equation for your exam):

Pressure = Force ÷ Area

<img src="/img/notes/02/pressure.png" alt="Turning Forces and Pressure, figure 1" /></a>

Pressure is measured in Newtons per square metre (N/m2) or Pascals (Pa)

The larger the force the greater the pressure.

The larger the area the lower the pressure.

<img src="/img/notes/02/Snowshoe.png" alt="Turning Forces and Pressure, figure 2" /></a>

Snow shoes can make it easier to walk on snow because they have a larger surface area than a normal shoe. This means that the weight of the person is spread out over a greater area of snow, meaning less pressure is applied to the snow. Therefore, the person will not sink into the snow as much, making it easier to walk

Worked Example

<img src="/img/notes/02/pressure-calc.png" alt="Turning Forces and Pressure, figure 3" /></a>

<h2 id="volume">Volume</h2>

The smaller the volume, the greater the pressure. The same amount of air molecules in a smaller volume will exert more pressure as there will be more collisions.

<img src="/img/notes/02/pressure-volume-1004x1024.jpg" alt="Turning Forces and Pressure, figure 1" /></a>

<h2 id="gas-pressure">Gas Pressure</h2>

<ol>
 <li>Atmospheric pressure is due to air molecules colliding with surfaces.</li>
 <li>Each collision exerts a tiny force on a surface but there are billions of collisions each second.</li>
</ol>

<img src="/img/notes/02/gas-pressure.png" alt="Turning Forces and Pressure, figure 1" /></a>

<ol>
 <li>Pressure can be changed by</li>
 <li>Changing the volume for the same amount of air (eg compressing)</li>
 <li>Changing the temperature</li>
 <li>Changing the number of air molecules (eg sucking air out of a container)</li>
</ol>

<h2 id="density">Density</h2>

Reducing the density of air particles in a container (sucking air out) will reduce the pressure in the container as there are less collisions.

A lower in pressure inside the container will mean that here is a larger force being applied outside the container, which could result in crushing the container.

Video - Crushing steel drum</a>

<h2 id="temperature">Temperature</h2>

The higher the temperature, the greater the pressure. Increasing the temperature of a gas will increase the pressure as the particles move faster, causing more frequent collisions.

<img src="/img/notes/02/pressure-temp.png" alt="Turning Forces and Pressure, figure 1" /></a>

<h2 id="altitude">Altitude</h2>

Atmospheric pressure changes with height above sea level. The higher the altitude, the lower the pressure.

The equation linking altitude and pressure is the same as the fluid pressure equation (you do NOT need to remember this equation for the exam):

p = hρg

p = pressure (Pa)

h = height (m)

ρ = density (kg/m3) **be careful as this looks a lot like p!**

g = gravitational field strength (N/kg)

A difference in pressure between two areas will cause a force to be exerted on the barrier between them. For example, the air pressure inside an aeroplane flying at 30,000ft is much higher than the air pressure outside the plane. This means that a force is exerted on the windows, doors and walls. The plane needs to be built to withstand these forces.

The size of the force can be calculated using this equation (you do NOT need to remember this equation for your exam):

F = ∆p x a

F = force (N)

∆p = pressure difference (Pa)

a = area (m2)

<dl>
	<dt>What moment is caused by a force of 5N acting 4m from the pivot?</dt>
	<dd id="Altitude0" class="js-click-to-reveal">Your answer should include: 20Nm / 20 Explanation: 20Nm</dd>
	<dt>A boy of weight 40N is sitting 0.5m away from the pivot of a see-saw. How far away from the pivot on the other side would a girl of weight 25N need to sit in order to balance the see-saw?</dt>
	<dd id="Altitude1" class="js-click-to-reveal">Your answer should include: 0.8m / 0.8 Explanation: 0.8m</dd>
	<dt>A box has a weight of 180N and a base of area 0.09m2. What pressure does it exert on the ground?</dt>
	<dd id="Altitude2" class="js-click-to-reveal">Your answer should include: 2000Pa / 2000 Explanation: 2000Pa</dd>
	<dt>Calculate the pressure exerted by a concrete slab of area 20m2 with a weight of 160,000N.</dt>
	<dd id="Altitude3" class="js-click-to-reveal">Your answer should include: 8000Pa / 8000 Explanation: 8000Pa</dd>
	<dt>A plug with an area of 0.005m2 is used in a bath which is filled with water to a depth of 0.4m. Calculate the pressure on the plug due to the water.</dt>
	<dd id="Altitude4" class="js-click-to-reveal">Your answer should include: 3920Pa / 3920 Explanation: 3920Pa</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Turning Forces and Pressure</h1>
</header>

<main class="blog-post__content">
	<h2 id="moments">Moments</h2>

	A moment is a turning force. The size of a moment can be calculated using this equation (you DO need to remember this equation for your exam):

	Moment = force x distance from pivot

	The moment can be increased by:

	<ol>
		<li>Increasing the size of the force</li>
		<li>Increasing the distance from the pivot</li>
	</ol>

	Objects will balance if the clockwise moment equals the anticlockwise moment.

	For an object in equilibrium (you do NOT need to remember this equation for your exam):

	W1d1 = W2d2

	W = weight (force) (N)

	d = distance from pivot (m)

	Worked Example

	What force is needed at A to balance the beam?

	<img src="/img/notes/02/moments.png" alt="Turning Forces and Pressure, figure 1" />

	Clockwise moment = 6 x 4 = 24Nm

	Anticlockwise moment = 8 x 2 = 16Nm

	For beam to balance, anticlockwise moment must be 24Nm

	Moment at A must be 8Nm (16 + 8 = 24Nm)

	Force A = moment ÷ distance

	Force A = 8 ÷ 4 = 2N

	<h2 id="centre-of-mass">Centre of Mass</h2>

	Equilibrium - An object is in equilibrium when the opposing forces on it are balanced.

	Centre of mass - The point on an object through which the weight of the object acts.

	For a regular, symmetrical shape with its mass evenly distributed, the centre of mass will be in the middle of the object:

	<img src="/img/notes/02/cm1.png" alt="Turning Forces and Pressure, figure 1" />

	If the mass is not evenly distributed, the centre of mass will not be in the centre of the object:

	<img src="/img/notes/02/cm2.png" alt="Turning Forces and Pressure, figure 2" />

	An object will balance at its centre of mass.

	An object will always come to rest with its centre of mass vertically below the point of suspension.

	<img src="/img/notes/02/cm3.png" alt="Turning Forces and Pressure, figure 3" />

	An object will fall over if its centre of mass moves outside the area of its base:

	<img src="/img/notes/02/cm4.png" alt="Turning Forces and Pressure, figure 4" />

	<h2 id="levers">Levers</h2>

	A lever is a simple machine that uses moments (turning forces) to make a task easier.

	There are two factors that can affect the lever:

	<ol>
		<li>The force applied to it (effort)</li>
		<li>The distance from the pivot</li>
	</ol>

	There are two types of lever:

	<ol>
		<li>Force multiplier - A small effort can be used to move a large load, but has to move a greater distance</li>
		<li>Distance multiplier - A small movement of the effort results in a large movement of the load, but a larger force has to be used</li>
	</ol>

	Example:

	<img src="/img/notes/02/l1.png" alt="Turning Forces and Pressure, figure 1" />

	The applied force is further away from the pivot than the exerted force. This means the force exerted will be greater than the force that was applied

	You should be able to identify the effort (input force), pivot, and load (output force) for a variety of examples of levers:

	<img src="/img/notes/02/l3-289x300.png" alt="Turning Forces and Pressure, figure 2" />

	<img src="/img/notes/02/l2.png" alt="Turning Forces and Pressure, figure 3" /><img src="/img/notes/02/l5.png" alt="Turning Forces and Pressure, figure 4" />

	<img src="/img/notes/02/l4.png" alt="Turning Forces and Pressure, figure 5" />

	<img src="/img/notes/02/l6.png" alt="Turning Forces and Pressure, figure 6" />

	<h2 id="gears">Gears</h2>

	Gears multiply the effect of a turning force

	<img src="/img/notes/02/gears-gif1.gif" alt="Turning Forces and Pressure, figure 1" />

	Low Gear:

	<ol>
		<li>Small wheel used to turn large wheel</li>
		<li>Low speed, high turning force</li>
	</ol>

	<img src="/img/notes/02/gears2.gif" alt="Turning Forces and Pressure, figure 2" />

	High Gear:

	<ol>
		<li>Large wheel used to turn small wheel</li>
		<li>High Speed, low turning force</li>
	</ol>

	Worked Example

	A gear wheel of radius 30mm is used to turn another gear wheel of radius 15mm with a force of 90N

	Calculate the moment of the force on:

	<ol>
		<li>The 15mm wheel</li>
		<li>The 30mm wheel</li>
	</ol>

	a)

	Moment = force x distance from pivot

	(distance from pivot = radius of gear wheel)

	Moment = 90 x 15 = 1350 Nmm (or 1.35Nm)

	b)

	Moment = force x distance from pivot

	(distance from pivot = radius of gear wheel)

	Moment = 90 x 30 = 2700 Nmm (or 2.7Nm)

	<h2 id="pressure-in-liquids">Pressure in Liquids</h2>

	Pressure in liquids increases with depth. If a container of water has three holes in the side, the water will shoot out further from the lowest hole because the pressure is greatest at the bottom of the container.

	<img src="/img/notes/02/liquid-pressure.png" alt="Turning Forces and Pressure, figure 1" />

	Pressure in liquids also depends on the density of the liquid. The relationship between pressure, density, and depth can be shown by this equation (you do NOT need to remember this equation for the exam):

	p = hρg

	p = pressure (Pa)

	h = height (m)

	ρ = density (kg/m3) **be careful as this looks a lot like p!**

	g = gravitational field strength (N/kg)

	Worked Example

	Calculate the pressure of sea water (density 1050 kg/m3) at a depth of 100m. (g = 9.8 N/kg)

	pressure = hρg

	pressure = 100 x 1050 x 9.8

	pressure = 1,029,000 Pa

	<h2 id="pressure">Pressure</h2>

	Surface Pressure

	Pressure is a force acting on an area. Pressure can be calculated using the following equation (you DO need to remember this equation for your exam):

	Pressure = Force ÷ Area

	<img src="/img/notes/02/pressure.png" alt="Turning Forces and Pressure, figure 1" />

	Pressure is measured in Newtons per square metre (N/m2) or Pascals (Pa)

	The larger the force, the greater the pressure.

	The larger the area, the lower the pressure.

	<img src="/img/notes/02/Snowshoe.png" alt="Turning Forces and Pressure, figure 2" />

	Snow shoes can make it easier to walk on snow because they have a larger surface area than a normal shoe. This means that the weight of the person is spread out over a greater area of snow, meaning less pressure is applied to the snow. Therefore, the person will not sink into the snow as much, making it easier to walk

	Worked Example

	<img src="/img/notes/02/pressure-calc.png" alt="Turning Forces and Pressure, figure 3" />

	<h2 id="volume">Volume</h2>

	The smaller the volume, the greater the pressure. The same amount of air molecules in a smaller volume will exert more pressure as there will be more collisions.

	<img src="/img/notes/02/pressure-volume-1004x1024.jpg" alt="Turning Forces and Pressure, figure 1" />

	<h2 id="gas-pressure">Gas Pressure</h2>

	<ol>
		<li>Atmospheric pressure is due to air molecules colliding with surfaces.</li>
		<li>Each collision exerts a tiny force on a surface, but there are billions of collisions each second.</li>
	</ol>

	<img src="/img/notes/02/gas-pressure.png" alt="Turning Forces and Pressure, figure 1" />

	<ol>
		<li>Pressure can be changed by</li>
		<li>Changing the volume for the same amount of air (e.g., compressing)</li>
		<li>Changing the temperature</li>
		<li>Changing the number of air molecules (e.g., sucking air out of a container)</li>
	</ol>

	<h2 id="density">Density</h2>

	Reducing the density of air particles in a container (sucking air out) will reduce the pressure in the container as there are fewer collisions.

	A lower pressure inside the container will mean that there is a larger force being applied outside the container, which could result in crushing the container.

	Video - <a href="http://www.youtube.com/watch?v=JsoE4F2Pb20" target="_blank">Crushing steel drum</a>

	<h2 id="temperature">Temperature</h2>

	The higher the temperature, the greater the pressure. Increasing the temperature of a gas will increase the pressure as the particles move faster, causing more frequent collisions.

	<img src="/img/notes/02/pressure-temp.png" alt="Turning Forces and Pressure, figure 1" />

	<h2 id="altitude">Altitude</h2>

	Atmospheric pressure changes with height above sea level. The higher the altitude, the lower the pressure.

	The equation linking altitude and pressure is the same as the fluid pressure equation (you do NOT need to remember this equation for the exam):

	p = hρg

	p = pressure (Pa)

	h = height (m)

	ρ = density (kg/m3) **be careful as this looks a lot like p!**

	g = gravitational field strength (N/kg)

	A difference in pressure between two areas will cause a force to be exerted on the barrier between them. For example, the air pressure inside an airplane flying at 30,000ft is much higher than the air pressure outside the plane. This means that a force is exerted on the windows, doors, and walls. The plane needs to be built to withstand these forces.

	The size of the force can be calculated using this equation (you do NOT need to remember this equation for your exam):

	F = ∆p x a

	F = force (N)

	∆p = pressure difference (Pa)

	a = area (m2)

	<dl>
		<dt>What moment is caused by a force of 5N acting 4m from the pivot?</dt>
		<dd id="Altitude0" class="js-click-to-reveal">Your answer should include: 20Nm / 20 Explanation: 20Nm</dd>
		<dt>A boy of weight 40N is sitting 0.5m away from the pivot of a see-saw. How far away from the pivot on the other side would a girl of weight 25N need to sit in order to balance the see-saw?</dt>
		<dd id="Altitude1" class="js-click-to-reveal">Your answer should include: 0.8m / 0.8 Explanation: 0.8m</dd>
		<dt>A box has a weight of 180N and a base of area 0.09m2. What pressure does it exert on the ground?</dt>
		<dd id="Altitude2" class="js-click-to-reveal">Your answer should include: 2000Pa / 2000 Explanation: 2000Pa</dd>
		<dt>Calculate the pressure exerted by a concrete slab of area 20m2 with a weight of 160,000N.</dt>
		<dd id="Altitude3" class="js-click-to-reveal">Your answer should include: 8000Pa / 8000 Explanation: 8000Pa</dd>
		<dt>A plug with an area of 0.005m2 is used in a bath which is filled with water to a depth of 0.4m. Calculate the pressure on the plug due to the water.</dt>
		<dd id="Altitude4" class="js-click-to-reveal">Your answer should include: 3920Pa / 3920 Explanation: 3920Pa</dd>
	</dl>
</main>

Turning Forces and Pressure

Forces

<header>
			<h1 class="blog-post__title">Motion</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="speed-and-acceleration">Speed and Acceleration</h2>

Speed (scalar): The distance covered per unit of time

Velocity (vector): Speed in a given direction

Velocity (or speed) can be calculated using this equation (you DO need to remember this equation in your exam):

<h2 class="ql-align-center">s = vt</h2>

s = distance (m) **be careful here as it is easy to assume ‘s’ stands for speed!**

__v __= velocity (m/s)

__t __= time (s)

Acceleration can be calculated using this equation (you DO need to remember this equation in your exam):

<h2 class="ql-align-center">a = Δv ÷ Δt</h2>

a = acceleration

Δv = change in velocity

Δt = change in time

Acceleration is measured in m/s2

Worked Example

A bus accelerates from 5 m/s to 25 m/s in 10s. What is it’s acceleration?

∆v = 25 – 5 = 20m/s

∆t = 10s

A = 20 ÷ 10 = 2 m/s2

Acceleration can also be calculated using this equation (you do NOT need to remember this equation in your exam):

<h2 class="ql-align-center">v2 – u2 = 2as</h2>

v = final velocity

u = initial velocity

a = acceleration

s = distance

Worked Example

A bus accelerates from 5 m/s to 25 m/s in 10s. How far does it travel during this time?

a = 2 m/s2 (from ∆v ÷∆t)

v2 - u2 = 2as

s = (v2 - u2) ÷ 2a

s = (252 – 52) ÷ 4

s = 150m

<h2 id="required-practical--acceleration">Required Practical – Acceleration</h2>

You need to be familiar with the method used to investigate the effect of force (or mass) on the acceleration of an object.

<img src="/img/notes/02/accel-practical.png" alt="Motion, figure 1" /></a>

If you are investigating force, then the number of masses on the end of the string should be changed but the mass of the trolley should remain constant.

If you are investigating mass, then the number of masses on the trolley should be changed but the mass on the end of the string should remain constant.

Examples:

Video 1</a>

Video 2</a>

<h2 id="velocity-time-graphs">Velocity-Time Graphs</h2>

A velocity-time graph can look very similar to a distance-time graph but it represents different motion, so make sure you check the axes of the graph on any question so you know which one you are dealing with.

<img src="/img/notes/02/vt-graph.png" alt="Motion, figure 1" /></a>

To calculate the distance travelled during a section of a velocity-time graph, calculate the area under that section of the graph

<img src="/img/notes/02/vt-distance.png" alt="Motion, figure 2" /></a>

Momentum

Momentum can be calculated using the following equation (you DO need to remember this for your exam):

<h3 class="ql-align-center">p = mv</h3>

__p __= momentum (kgm/s)

m = mass (kg)

v = velocity (m/s)

With momentum (and velocity), + and – signs are used to indicate direction. For example, a car travelling with a momentum of -100kgm/s has the same momentum as a car with 100kgm/s but it is travelling in the opposite direction.

<h2 id="distance-time-graphs">Distance-Time Graphs</h2>

Distance (scalar): How much ground an object has covered during its motion

Displacement (vector): The overall change in position of an object

<img src="/img/notes/02/distance.png" alt="Motion, figure 1" /></a>

You need to be able to interpret the shape of a distance-time graph

<img src="/img/notes/02/dt-graph.png" alt="Motion, figure 2" /></a>

To calculate the speed from a distance time graph, work out the gradient of the line

<img src="/img/notes/02/dt-graph-speed.png" alt="Motion, figure 3" /></a>

To calculate the speed during a period of acceleration, draw a tangent to the curve and calculate the gradient of the tangent

<img src="/img/notes/02/dt-tangent.png" alt="Motion, figure 4" /></a>

<h2 id="momentum">Momentum</h2>

Typical speeds:

<ol>
 <li>Walking 1.5m/s</li>
 <li>Running 3m/s</li>
 <li>Cycling 6m/s</li>
 <li>Sound 330m/s</li>
</ol>

<h2 id="conservation-of-momentum">Conservation of Momentum</h2>

The principle of conservation of momentum is that the total momentum of s group of objects before a collision is equal to the total momentum after the collision.

Example 1 – two objects that join together after colliding:

<img src="/img/notes/02/m1.png" alt="Motion, figure 1" /></a>

<img src="/img/notes/02/m2.png" alt="Motion, figure 2" /></a>

Example 2 – two objects collide and bounce off each other:

<img src="/img/notes/02/m3.png" alt="Motion, figure 3" /></a>

<img src="/img/notes/02/m4.png" alt="Motion, figure 4" /></a>

(NB a total momentum of zero between the two objects does not mean they are not moving, but that they are moving with equal momentum in opposite directions.)

Worked Example 1

Trolley A has a mass of 1.5kg and is pushed into trolley B at a velocity of 2.2m/s. Trolley B has a mass of 0.5kg and is not moving. After the impact the trolleys stick together

Calculate:

<ol>
 <li>The momentum of trolley A before the impact</li>
 <li>The velocity of the two trolleys after the impact</li>
</ol>

<img src="/img/notes/02/m5.png" alt="Motion, figure 5" /></a>

1

<img src="/img/notes/02/m6.png" alt="Motion, figure 6" /></a>

Momentum = mass x velocity

Momentum = 1.5 x 2.2

Momentum = 3.3 kgm/s

2

<img src="/img/notes/02/m7.png" alt="Motion, figure 7" /></a>

Momentum before collision = 3.3 kgm/s

Therefore, Momentum after collision = 3.3 kgm/s (no calculation necessary, just use the principle of the conservation of momentum)

Velocity = momentum ÷ mass

Velocity = 3.3 ÷ 2

Velocity = 1.65 m/s

Worked Example 2

A man of mass 80kg jumps from a boat of mass 8000kg to the pier at a speed of 4m/s. Describe the motion of the boat.

<img src="/img/notes/02/m8.png" alt="Motion, figure 8" /></a>

<ol>
 <li>Total momentum before jump = 0 kgm/s</li>
 <li>Total momentum after jump = 0 kgm/s</li>
 <li>Man: momentum after jump = 320 kgm/s</li>
 <li>Boat: momentum after jump = -320 kgm/s</li>
 <li>Boat: velocity = -0.04m/s</li>
</ol>

<h2 id="changes-in-momentum">Changes in Momentum</h2>

To change the momentum of an object, a force is required. The relationship between force, change in momentum and the time taken for the momentum to change is shown by this equation (you do NOT need to remember this equation for the exam):

<h3 id="f--δp--t">F = Δp ÷ t</h3>

F = force (N)

Δp = momentum (kgm/s)

__t __= time (s)

In a car crash, there is a sudden change in momentum, which means there is a large force on the passengers. Increasing the time taken for the change in momentum will reduce the force on the passengers, therefore reducing the chance of injury.

Crumple Zone

<img src="/img/notes/02/crumple-zone.png" alt="Motion, figure 1" /></a>

The front of car is designed to crumple more easily than the rest, this is known as a crumple zone. The crumple zone means that the time taken to stop (in a crash) is slightly increased (change of momentum takes longer). This increase in time means that there is less force applied to the passenger and so there is less chance of injury.

Video - Physics of crumple zones</a>

Video - Crumple zones and momentum</a>

Seatbelt

<img src="/img/notes/02/seatbelt.png" alt="Motion, figure 2" /></a>

A seatbelt applies a force to slow you down in a collision as your body will continue moving forwards until a force is applied. It is made from a material that is strong enough to stop you before you hit steering wheel but that is also slightly flexible to increase time taken for change in momentum, reducing the chance of injury. It also spreads the force over a wider area of the body, reducing the pressure on any one particular part.

Video – Seat belt testing</a>

<h3 id="airbag">Airbag</h3>

<img src="/img/notes/02/airbag.jpg" alt="Motion, figure 3" /></a>

An airbag inflates in a collision to apply force to slow you down, before you hit the (harder) steering wheel or dashboard. It is made from a more flexible material than steering wheel which increases the time taken for change in momentum. This reduces the force on the passenger. The force is also spread out over a greater area of the body, reducing the pressure on any one particular part.

Video - Air bag</a>

Crash Helmet

<img src="/img/notes/02/crash-helmet.png" alt="Motion, figure 4" /></a>

A crash helmet is made from a more flexible material than your skull! This increases the time taken for the change in momentum, reducing the risk of injury. Some of the energy of the collision is dissipated in cracking the outer shell of the helmet, meaning less is transferred to your skull.

Video - Crash helmet</a>

<dl>
	<dt>A man travels 10m in 5s. What is his speed?</dt>
	<dd id="Changes-in-Momentum0" class="js-click-to-reveal">Your answer should include: 2m/s / 2 Explanation: 2m/s</dd>
	<dt>How long will it take for a plane to travel 1m if it's speed is 100m/s?</dt>
	<dd id="Changes-in-Momentum1" class="js-click-to-reveal">Your answer should include: 1ms / 1 Explanation: 1ms</dd>
	<dt>Calculate the acceleration of a car if increases its velocity from 0m/s to 15m/s in 3s.</dt>
	<dd id="Changes-in-Momentum2" class="js-click-to-reveal">5</dd>
	<dt>Calculate the momentum of an 80kg man running at 5m/s.</dt>
	<dd id="Changes-in-Momentum3" class="js-click-to-reveal">Your answer should include: 400kgm/s / 400 Explanation: 400kgm/s</dd>
	<dt>If a car accelerates at 5m/s2 from rest for 4s, what is its velocity?</dt>
	<dd id="Changes-in-Momentum4" class="js-click-to-reveal">Your answer should include: 20m/s / 20 Explanation: 20m/s</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Motion</h1>
</header>

<main class="blog-post__content">
	<h2 id="speed-and-acceleration">Speed and Acceleration</h2>

	Speed (scalar): The distance covered per unit of time.

	Velocity (vector): Speed in a given direction.

	Velocity (or speed) can be calculated using this equation (you DO need to remember this equation for your exam):

	<h2 class="ql-align-center">s = vt</h2>

	s = distance (m) **be careful here as it is easy to assume ‘s’ stands for speed!**

	v = velocity (m/s)

	t = time (s)

	Acceleration can be calculated using this equation (you DO need to remember this equation for your exam):

	<h2 class="ql-align-center">a = Δv ÷ Δt</h2>

	a = acceleration

	Δv = change in velocity

	Δt = change in time

	Acceleration is measured in m/s2.

	Worked Example

	A bus accelerates from 5 m/s to 25 m/s in 10s. What is its acceleration?

	∆v = 25 – 5 = 20m/s

	∆t = 10s

	a = 20 ÷ 10 = 2 m/s2

	Acceleration can also be calculated using this equation (you do NOT need to remember this equation for your exam):

	<h2 class="ql-align-center">v2 – u2 = 2as</h2>

	v = final velocity

	u = initial velocity

	a = acceleration

	s = distance

	Worked Example

	A bus accelerates from 5 m/s to 25 m/s in 10s. How far does it travel during this time?

	a = 2 m/s2 (from ∆v ÷∆t)

	v2 - u2 = 2as

	s = (v2 - u2) ÷ 2a

	s = (252 – 52) ÷ 4

	s = 150m

	<h2 id="required-practical--acceleration">Required Practical – Acceleration</h2>

	You need to be familiar with the method used to investigate the effect of force (or mass) on the acceleration of an object.

	<a href="/img/notes/02/accel-practical.png" target="_blank"><img src="/img/notes/02/accel-practical.png" alt="Motion, figure 1" /></a>

	If you are investigating force, then the number of masses on the end of the string should be changed but the mass of the trolley should remain constant.

	If you are investigating mass, then the number of masses on the trolley should be changed but the mass on the end of the string should remain constant.

	<h2 id="velocity-time-graphs">Velocity-Time Graphs</h2>

	A velocity-time graph can look very similar to a distance-time graph but it represents different motion, so make sure you check the axes of the graph on any question so you know which one you are dealing with.

	<a href="/img/notes/02/vt-graph.png" target="_blank"><img src="/img/notes/02/vt-graph.png" alt="Motion, figure 1" /></a>

	To calculate the distance travelled during a section of a velocity-time graph, calculate the area under that section of the graph.

	<a href="/img/notes/02/vt-distance.png" target="_blank"><img src="/img/notes/02/vt-distance.png" alt="Motion, figure 2" /></a>

	Momentum

	Momentum can be calculated using the following equation (you DO need to remember this for your exam):

	<h3 class="ql-align-center">p = mv</h3>

	p = momentum (kgm/s)

	m = mass (kg)

	v = velocity (m/s)

	With momentum (and velocity), + and – signs are used to indicate direction. For example, a car travelling with a momentum of -100kgm/s has the same momentum as a car with 100kgm/s but it is travelling in the opposite direction.

	<h2 id="distance-time-graphs">Distance-Time Graphs</h2>

	Distance (scalar): How much ground an object has covered during its motion.

	Displacement (vector): The overall change in position of an object.

	<a href="/img/notes/02/distance.png" target="_blank"><img src="/img/notes/02/distance.png" alt="Motion, figure 1" /></a>

	You need to be able to interpret the shape of a distance-time graph.

	<a href="/img/notes/02/dt-graph.png" target="_blank"><img src="/img/notes/02/dt-graph.png" alt="Motion, figure 2" /></a>

	To calculate the speed from a distance-time graph, work out the gradient of the line.

	<a href="/img/notes/02/dt-graph-speed.png" target="_blank"><img src="/img/notes/02/dt-graph-speed.png" alt="Motion, figure 3" /></a>

	To calculate the speed during a period of acceleration, draw a tangent to the curve and calculate the gradient of the tangent.

	<a href="/img/notes/02/dt-tangent.png" target="_blank"><img src="/img/notes/02/dt-tangent.png" alt="Motion, figure 4" /></a>

	<h2 id="momentum">Momentum</h2>

	Typical speeds:

	<ol>
		<li>Walking 1.5m/s</li>
		<li>Running 3m/s</li>
		<li>Cycling 6m/s</li>
		<li>Sound 330m/s</li>
	</ol>

	<h2 id="conservation-of-momentum">Conservation of Momentum</h2>

	The principle of conservation of momentum is that the total momentum of a group of objects before a collision is equal to the total momentum after the collision.

	Example 1 – two objects that join together after colliding:

	<a href="/img/notes/02/m1.png" target="_blank"><img src="/img/notes/02/m1.png" alt="Motion, figure 1" /></a>

	<a href="/img/notes/02/m2.png" target="_blank"><img src="/img/notes/02/m2.png" alt="Motion, figure 2" /></a>

	Example 2 – two objects collide and bounce off each other:

	<a href="/img/notes/02/m3.png" target="_blank"><img src="/img/notes/02/m3.png" alt="Motion, figure 3" /></a>

	<a href="/img/notes/02/m4.png" target="_blank"><img src="/img/notes/02/m4.png" alt="Motion, figure 4" /></a>

	(NB a total momentum of zero between the two objects does not mean they are not moving, but that they are moving with equal momentum in opposite directions.)

	Worked Example 1

	Trolley A has a mass of 1.5kg and is pushed into trolley B at a velocity of 2.2m/s. Trolley B has a mass of 0.5kg and is not moving. After the impact, the trolleys stick together.

	Calculate:

	<ol>
		<li>The momentum of trolley A before the impact</li>
		<li>The velocity of the two trolleys after the impact</li>
	</ol>

	<a href="/img/notes/02/m5.png" target="_blank"><img src="/img/notes/02/m5.png" alt="Motion, figure 5" /></a>

	1

	<a href="/img/notes/02/m6.png" target="_blank"><img src="/img/notes/02/m6.png" alt="Motion, figure 6" /></a>

	Momentum = mass x velocity

	Momentum = 1.5 x 2.2

	Momentum = 3.3 kgm/s

	2

	<a href="/img/notes/02/m7.png" target="_blank"><img src="/img/notes/02/m7.png" alt="Motion, figure 7" /></a>

	Momentum before collision = 3.3 kgm/s

	Therefore, Momentum after collision = 3.3 kgm/s (no calculation necessary, just use the principle of the conservation of momentum)

	Velocity = momentum ÷ mass

	Velocity = 3.3 ÷ 2

	Velocity = 1.65 m/s

	Worked Example 2

	A man of mass 80kg jumps from a boat of mass 8000kg to the pier at a speed of 4m/s. Describe the motion of the boat.

	<a href="/img/notes/02/m8.png" target="_blank"><img src="/img/notes/02/m8.png" alt="Motion, figure 8" /></a>

	<ol>
		<li>Total momentum before jump = 0 kgm/s</li>
		<li>Total momentum after jump = 0 kgm/s</li>
		<li>Man: momentum after jump = 320 kgm/s</li>
		<li>Boat: momentum after jump = -320 kgm/s</li>
		<li>Boat: velocity = -0.04m/s</li>
	</ol>

	<h2 id="changes-in-momentum">Changes in Momentum</h2>

	To change the momentum of an object, a force is required. The relationship between force, change in momentum, and the time taken for the momentum to change is shown by this equation (you do NOT need to remember this equation for the exam):

	<h3 id="f--δp--t">F = Δp ÷ t</h3>

	F = force (N)

	Δp = change in momentum (kgm/s)

	t = time (s)

	In a car crash, there is a sudden change in momentum, which means there is a large force on the passengers. Increasing the time taken for the change in momentum will reduce the force on the passengers, therefore reducing the chance of injury.

	Crumple Zone

	<a href="/img/notes/02/crumple-zone.png" target="_blank"><img src="/img/notes/02/crumple-zone.png" alt="Motion, figure 1" /></a>

	The front of the car is designed to crumple more easily than the rest; this is known as a crumple zone. The crumple zone means that the time taken to stop (in a crash) is slightly increased (change of momentum takes longer). This increase in time means that there is less force applied to the passenger and so there is less chance of injury.

	Seatbelt

	<a class="img-20" href="/img/notes/02/seatbelt.png" target="_blank"><img class="img-20" src="/img/notes/02/seatbelt.png" alt="Motion, figure 2" /></a>

	A seatbelt applies a force to slow you down in a collision as your body will continue moving forwards until a force is applied. It is made from a material that is strong enough to stop you before you hit the steering wheel but that is also slightly flexible to increase the time taken for the change in momentum, reducing the chance of injury. It also spreads the force over a wider area of the body, reducing the pressure on any one particular part.

	<h3 id="airbag">Airbag</h3>

	<a href="/img/notes/02/airbag.jpg" target="_blank"><img src="/img/notes/02/airbag.jpg" alt="Motion, figure 3" /></a>

	An airbag inflates in a collision to apply force to slow you down before you hit the (harder) steering wheel or dashboard. It is made from a more flexible material than the steering wheel, which increases the time taken for the change in momentum. This reduces the force on the passenger. The force is also spread out over a greater area of the body, reducing the pressure on any one particular part.

	Crash Helmet

	<a class="img-20" href="/img/notes/02/crash-helmet.png" target="_blank"><img class="img-20" src="/img/notes/02/crash-helmet.png" alt="Motion, figure 4" /></a>

	A crash helmet is made from a more flexible material than your skull! This increases the time taken for the change in momentum, reducing the risk of injury. Some of the energy of the collision is dissipated in cracking the outer shell of the helmet, meaning less is transferred to your skull.

	<dl>
		<dt>A man travels 10m in 5s. What is his speed?</dt>
		<dd id="Changes-in-Momentum0" class="js-click-to-reveal">Your answer should include: 2m/s / 2 Explanation: 2m/s</dd>
		<dt>How long will it take for a plane to travel 1m if its speed is 100m/s?</dt>
		<dd id="Changes-in-Momentum1" class="js-click-to-reveal">Your answer should include: 1ms / 1 Explanation: 1ms</dd>
		<dt>Calculate the acceleration of a car if it increases its velocity from 0m/s to 15m/s in 3s.</dt>
		<dd id="Changes-in-Momentum2" class="js-click-to-reveal">5</dd>
		<dt>Calculate the momentum of an 80kg man running at 5m/s.</dt>
		<dd id="Changes-in-Momentum3" class="js-click-to-reveal">Your answer should include: 400kgm/s / 400 Explanation: 400kgm/s</dd>
		<dt>If a car accelerates at 5m/s2 from rest for 4s, what is its velocity?</dt>
		<dd id="Changes-in-Momentum4" class="js-click-to-reveal">Your answer should include: 20m/s / 20 Explanation: 20m/s</dd>
	</dl>
</main>

Motion

<header>
			<h1 class="blog-post__title">Forces in Action</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="friction">Friction</h2>

Friction is a force that occurs between two surfaces which are in contact and trying to move past each other. Friction acts in the opposite direction to the motion. Energy used against friction is transformed to heat. The temperature of the object and surface will increase.

<img src="/img/notes/02/friction-300x192.png" alt="Forces in Action, figure 1" /></a>

<h2 id="work-done">Work Done</h2>

Work done is a measurement of how much energy is required to move an object. It can be calculated using the equation (you DO need to remember this equation for your exam):

W = Fs

W = work done (J)

F = force (N)

__s __= distance (m)

<img src="/img/notes/02/work.png" alt="Forces in Action, figure 1" /></a>

Worked Example

A race up Ben Nevis starts in a car park 50m above sea level. The top of Ben Nevis is 1344m. Chris weighs 600N and Alison weighs 400N. Calculate the work done by each of them during the race.

<ol>
 <li>Distance climbed = 1294m</li>
 <li>Chris: work done = 600 x 1294 = 776,400 J</li>
 <li>Alison: work done = 400 x 1294 = 517,600J</li>
 <li>Chris needs more energy for the climb because he weighs more</li>
</ol>

<h2 id="elasticity">Elasticity</h2>

<ol>
 <li>A force can cause an object to change shape</li>
 <li>Elastic materials store Elastic Potential Energy</li>
 <li>The EPE is released when the object springs back to it’s normal shape</li>
</ol>

For example, in a catapult

<img src="/img/notes/02/catapult.png" alt="Forces in Action, figure 1" /></a>

<ol>
 <li>Work done/energy used to stretch catapult</li>
 <li>EPE stored in the catapult while it is stretched</li>
 <li>EPE released (transformed into Kinetic Energy) when the catapult is released</li>
</ol>

Or, in a squash ball

<img src="/img/notes/02/squash-300x204.png" alt="Forces in Action, figure 2" /></a>

<ol>
 <li>Work done/energy used to squash ball</li>
 <li>EPE stored in the ball while it is squashed</li>
 <li>EPE released (transformed into Kinetic Energy) when the ball is released</li>
</ol>

<h2 id="hookes-law">Hooke’s Law</h2>

The extension of an elastic object is proportional to the force acting on it.

This can be represented by the equation (you DO need to remember this equation for your exam):

<ol>
 <li>__F __= k x e</li>
 <li>__F __= force (N)</li>
 <li>k = spring constant (N/m)</li>
 <li>e = extension (m)</li>
</ol>

<img src="/img/notes/02/hookes-law-300x229.png" alt="Forces in Action, figure 1" /></a>

<ol>
 <li>The extension of an elastic object is proportional to the force acting on it until it reaches it’s elastic limit (limit of proportionality)</li>
 <li>After the elastic limit, the object no longer returns to it’s original shape</li>
</ol>

<img src="/img/notes/02/elastic-limit-300x204.png" alt="Forces in Action, figure 2" /></a>

<h2 id="required-practical--elasticity">Required Practical – Elasticity</h2>

You need to be familiar with the practical method to investigate the relationship between force and extension (Hooke’s law)

<img src="/img/notes/02/elasticity-practical-300x292.png" alt="Forces in Action, figure 1" /></a>

Using an elastic material, such as a spring, add masses to the spring and measure the extension with each mass added.

Plotting a graph of force and extension should produce a directly proportional line as shown in the Hooke’s law section above. The gradient of the line is equal to the spring constant of the spring used In the experiment.

Possible causes of error in the experiment include:

<ol>
 <li>Inaccurate measurement of the length or extension due to human error</li>
 <li>Stretching the spring past it’s elastic limit, at which point the relationship between force and extension is no longer proportional and the spring does not return to it’s original size when the masses are removed</li>
</ol>

<h2 id="vector-diagrams">Vector Diagrams</h2>

The resultant force on an object is is the sum of all the forces acting on an object. If the forces acting on the object are not all acting on the same line, vector diagrams can be used to find the resultant force.

<img src="/img/notes/02/vectors1-300x156.png" alt="Forces in Action, figure 1" /></a>

Vector diagrams are __drawn to scale. __The length of the arrow equals the size of the force (eg 2cm = 2N).

<img src="/img/notes/02/v2-300x124.png" alt="Forces in Action, figure 2" /></a>Draw first force to scale.

<img src="/img/notes/02/v3-300x141.png" alt="Forces in Action, figure 3" /></a>

Draw second force at the end of the other (using the same scale and at the correct angle)

<img src="/img/notes/02/v4.png" alt="Forces in Action, figure 4" /></a>

The resultant force is shown by the line from the starting point to the ending point of your diagram

Worked Example

A tow rope is attached to a car at two points 1m apart at 35o to each other. If the pull on each attachment is 3000N, what is the force on the main tow rope?

<img src="/img/notes/02/v5.png" alt="Forces in Action, figure 5" /></a>

Choose appropriate scale (eg 1cm = 1000N)

<img src="/img/notes/02/v6.png" alt="Forces in Action, figure 6" /></a>

Draw first force to scale (3cm = 3000N)

<img src="/img/notes/02/v7.png" alt="Forces in Action, figure 7" /></a>

Draw second force at the end of the previous force (at 35o )

<img src="/img/notes/02/v8.png" alt="Forces in Action, figure 8" /></a>

Measure resultant line (5.7cm)

Resultant force = 5700N

<h2 id="stopping-distances">Stopping Distances</h2>

Vehicles do not stop instantly. During the time they take to stop, they are still travelling. This distance travelled is known as the stopping distance.

The stopping distance is made up of the thinking distance and the braking distance:

<ol>
 <li>Thinking Distance - The distance travelled in the time it takes the driver to react</li>
 <li>Braking Distance - The distance travelled after the brakes have been pressed</li>
 <li>Stopping Distance = Thinking distance + braking distance</li>
</ol>

<img src="/img/notes/02/stopping.png" alt="Forces in Action, figure 1" /></a>

Factors affecting thinking distance:

<ol>
 <li>Alcohol/Drugs</li>
 <li>Tiredness</li>
 <li>Age</li>
 <li>Speed</li>
 <li>Distractions may prevent the driver stopping as quickly but have not affected his/her reaction time directly</li>
</ol>

Factors affecting braking distance:

<ol>
 <li>Brake condition</li>
 <li>Surface</li>
 <li>Tyres</li>
 <li>Weather – ice/rain</li>
 <li>Speed</li>
</ol>

Thinking distance increases in linear relationship with speed. Thinking distance = speed x time

<img src="/img/notes/02/thinking-300x226.png" alt="Forces in Action, figure 2" /></a>

Braking distance increases in a squared relationship with speed. If the speed doubles, the braking distance increases 4 times

<img src="/img/notes/02/braking-300x218.png" alt="Forces in Action, figure 3" /></a>

<h2 id="resolving-forces">Resolving Forces</h2>

A force acting at an angle can be resolved into two perpendicular forces. Draw a scale diagram, with sides perpendicular to each other and with the original force as the diagonal. If drawn to scale, the sides of the rectangle can be measured to find the size of the force.

<img src="/img/notes/02/v9-300x250.png" alt="Forces in Action, figure 1" /></a>

Worked Example

A car of weight 10kN is parked on an uphill road. The road is inclined at an angle of 20o. Find the component of the car’s weight that acts down the slope.

<img src="/img/notes/02/v10-300x225.png" alt="Forces in Action, figure 2" /></a>Draw scale diagram

<img src="/img/notes/02/v11-300x235.png" alt="Forces in Action, figure 3" /></a>

Complete rectangle with original force as the diagonal

<img src="/img/notes/02/v12-300x231.png" alt="Forces in Action, figure 4" /></a>

Measure the component down the slope

Component down the slope = 3kN

<dl>
	<dt>A man pushes a car with a force of 550N for 12m. How much work was done?</dt>
	<dd id="Resolving-Forces0" class="js-click-to-reveal">Your answer should include: 6600J / 6600 Explanation: 6600J</dd>
	<dt>A child pulled a toy train across a room with a force of 6N. The child pulls the toy a distance of 4m. How much work does the child do?</dt>
	<dd id="Resolving-Forces1" class="js-click-to-reveal">Your answer should include: 24J / 24 Explanation: 24J</dd>
	<dt>A pupil investigates Hooke’s law for a spring. When a mass of 100g is hung on the spring, the total length of the spring is 12cm. When a 300g mass is hung on it, the total length of the spring is 16cm. How long will the spring be when 200g is hung on it?</dt>
	<dd id="Resolving-Forces2" class="js-click-to-reveal">Your answer should include: 14cm / 14 Explanation: 14cm</dd>
	<dt>What is the unstretched length of the spring in the previous question?</dt>
	<dd id="Resolving-Forces3" class="js-click-to-reveal">Your answer should include: 10cm / 10 Explanation: 10cm</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Forces in Action</h1>
</header>

<main class="blog-post__content">
	<h2 id="friction">Friction</h2>

	Friction is a force that occurs between two surfaces which are in contact and trying to move past each other. Friction acts in the opposite direction to the motion. Energy used against friction is transformed into heat. The temperature of the object and surface will increase.

	<a href="/img/notes/02/friction-300x192.png" target="_blank"><img src="/img/notes/02/friction-300x192.png" alt="Forces in Action, figure 1" /></a>

	<h2 id="work-done">Work Done</h2>

	Work done is a measurement of how much energy is required to move an object. It can be calculated using the equation (you DO need to remember this equation for your exam):

	W = Fs

	W = work done (J)

	F = force (N)

	s = distance (m)

	<a href="/img/notes/02/work.png" target="_blank"><img src="/img/notes/02/work.png" alt="Forces in Action, figure 1" /></a>

	Worked Example

	A race up Ben Nevis starts in a car park 50m above sea level. The top of Ben Nevis is 1344m. Chris weighs 600N and Alison weighs 400N. Calculate the work done by each of them during the race.

	<ol>
		<li>Distance climbed = 1294m</li>
		<li>Chris: work done = 600 x 1294 = 776,400 J</li>
		<li>Alison: work done = 400 x 1294 = 517,600 J</li>
		<li>Chris needs more energy for the climb because he weighs more</li>
	</ol>

	<h2 id="elasticity">Elasticity</h2>

	<ol>
		<li>A force can cause an object to change shape</li>
		<li>Elastic materials store Elastic Potential Energy</li>
		<li>The EPE is released when the object springs back to its normal shape</li>
	</ol>

	For example, in a catapult

	<a href="/img/notes/02/catapult.png" target="_blank"><img src="/img/notes/02/catapult.png" alt="Forces in Action, figure 1" /></a>

	<ol>
		<li>Work done/energy used to stretch catapult</li>
		<li>EPE stored in the catapult while it is stretched</li>
		<li>EPE released (transformed into Kinetic Energy) when the catapult is released</li>
	</ol>

	Or, in a squash ball

	<a href="/img/notes/02/squash-300x204.png" target="_blank"><img src="/img/notes/02/squash-300x204.png" alt="Forces in Action, figure 2" /></a>

	<ol>
		<li>Work done/energy used to squash ball</li>
		<li>EPE stored in the ball while it is squashed</li>
		<li>EPE released (transformed into Kinetic Energy) when the ball is released</li>
	</ol>

	<h2 id="hookes-law">Hooke’s Law</h2>

	The extension of an elastic object is proportional to the force acting on it.

	This can be represented by the equation (you DO need to remember this equation for your exam):

	<ol>
		<li>F = k x e</li>
		<li>F = force (N)</li>
		<li>k = spring constant (N/m)</li>
		<li>e = extension (m)</li>
	</ol>

	<a href="/img/notes/02/hookes-law-300x229.png" target="_blank"><img src="/img/notes/02/hookes-law-300x229.png" alt="Forces in Action, figure 1" /></a>

	<ol>
		<li>The extension of an elastic object is proportional to the force acting on it until it reaches its elastic limit (limit of proportionality)</li>
		<li>After the elastic limit, the object no longer returns to its original shape</li>
	</ol>

	<a href="/img/notes/02/elastic-limit-300x204.png" target="_blank"><img src="/img/notes/02/elastic-limit-300x204.png" alt="Forces in Action, figure 2" /></a>

	<h2 id="required-practical--elasticity">Required Practical – Elasticity</h2>

	You need to be familiar with the practical method to investigate the relationship between force and extension (Hooke’s law)

	<a href="/img/notes/02/elasticity-practical-300x292.png" target="_blank"><img src="/img/notes/02/elasticity-practical-300x292.png" alt="Forces in Action, figure 1" /></a>

	Using an elastic material, such as a spring, add masses to the spring and measure the extension with each mass added.

	Plotting a graph of force and extension should produce a directly proportional line as shown in the Hooke’s law section above. The gradient of the line is equal to the spring constant of the spring used in the experiment.

	Possible causes of error in the experiment include:

	<ol>
		<li>Inaccurate measurement of the length or extension due to human error</li>
		<li>Stretching the spring past its elastic limit, at which point the relationship between force and extension is no longer proportional and the spring does not return to its original size when the masses are removed</li>
	</ol>

	<h2 id="vector-diagrams">Vector Diagrams</h2>

	The resultant force on an object is the sum of all the forces acting on an object. If the forces acting on the object are not all acting on the same line, vector diagrams can be used to find the resultant force.

	<a href="/img/notes/02/vectors1-300x156.png" target="_blank"><img src="/img/notes/02/vectors1-300x156.png" alt="Forces in Action, figure 1" /></a>

	Vector diagrams are drawn to scale. The length of the arrow equals the size of the force (e.g. 2cm = 2N).

	<a href="/img/notes/02/v2-300x124.png" target="_blank"><img src="/img/notes/02/v2-300x124.png" alt="Forces in Action, figure 2" /></a>Draw first force to scale.

	<a href="/img/notes/02/v3-300x141.png" target="_blank"><img src="/img/notes/02/v3-300x141.png" alt="Forces in Action, figure 3" /></a>

	Draw second force at the end of the other (using the same scale and at the correct angle)

	<a href="/img/notes/02/v4.png" target="_blank"><img src="/img/notes/02/v4.png" alt="Forces in Action, figure 4" /></a>

	The resultant force is shown by the line from the starting point to the ending point of your diagram

	Worked Example

	A tow rope is attached to a car at two points 1m apart at 35o to each other. If the pull on each attachment is 3000N, what is the force on the main tow rope?

	<a href="/img/notes/02/v5.png" target="_blank"><img src="/img/notes/02/v5.png" alt="Forces in Action, figure 5" /></a>

	Choose appropriate scale (e.g. 1cm = 1000N)

	<a href="/img/notes/02/v6.png" target="_blank"><img src="/img/notes/02/v6.png" alt="Forces in Action, figure 6" /></a>

	Draw first force to scale (3cm = 3000N)

	<a href="/img/notes/02/v7.png" target="_blank"><img src="/img/notes/02/v7.png" alt="Forces in Action, figure 7" /></a>

	Draw second force at the end of the previous force (at 35o)

	<a href="/img/notes/02/v8.png" target="_blank"><img src="/img/notes/02/v8.png" alt="Forces in Action, figure 8" /></a>

	Measure resultant line (5.7cm)

	Resultant force = 5700N

	<h2 id="stopping-distances">Stopping Distances</h2>

	Vehicles do not stop instantly. During the time they take to stop, they are still travelling. This distance travelled is known as the stopping distance.

	The stopping distance is made up of the thinking distance and the braking distance:

	<ol>
		<li>Thinking Distance - The distance travelled in the time it takes the driver to react</li>
		<li>Braking Distance - The distance travelled after the brakes have been pressed</li>
		<li>Stopping Distance = Thinking distance + braking distance</li>
	</ol>

	<a href="/img/notes/02/stopping.png" target="_blank"><img src="/img/notes/02/stopping.png" alt="Forces in Action, figure 1" /></a>

	Factors affecting thinking distance:

	<ol>
		<li>Alcohol/Drugs</li>
		<li>Tiredness</li>
		<li>Age</li>
		<li>Speed</li>
		<li>Distractions may prevent the driver from stopping as quickly but have not affected his/her reaction time directly</li>
	</ol>

	Factors affecting braking distance:

	<ol>
		<li>Brake condition</li>
		<li>Surface</li>
		<li>Tyres</li>
		<li>Weather – ice/rain</li>
		<li>Speed</li>
	</ol>

	Thinking distance increases in a linear relationship with speed. Thinking distance = speed x time

	<a href="/img/notes/02/thinking-300x226.png" target="_blank"><img src="/img/notes/02/thinking-300x226.png" alt="Forces in Action, figure 2" /></a>

	Braking distance increases in a squared relationship with speed. If the speed doubles, the braking distance increases 4 times

	<a href="/img/notes/02/braking-300x218.png" target="_blank"><img src="/img/notes/02/braking-300x218.png" alt="Forces in Action, figure 3" /></a>

	<h2 id="resolving-forces">Resolving Forces</h2>

	A force acting at an angle can be resolved into two perpendicular forces. Draw a scale diagram, with sides perpendicular to each other and with the original force as the diagonal. If drawn to scale, the sides of the rectangle can be measured to find the size of the force.

	<a href="/img/notes/02/v9-300x250.png" target="_blank"><img src="/img/notes/02/v9-300x250.png" alt="Forces in Action, figure 1" /></a>

	Worked Example

	A car of weight 10kN is parked on an uphill road. The road is inclined at an angle of 20o. Find the component of the car’s weight that acts down the slope.

	<a href="/img/notes/02/v10-300x225.png" target="_blank"><img src="/img/notes/02/v10-300x225.png" alt="Forces in Action, figure 2" /></a>Draw scale diagram

	<a href="/img/notes/02/v11-300x235.png" target="_blank"><img src="/img/notes/02/v11-300x235.png" alt="Forces in Action, figure 3" /></a>

	Complete rectangle with original force as the diagonal

	<a href="/img/notes/02/v12-300x231.png" target="_blank"><img src="/img/notes/02/v12-300x231.png" alt="Forces in Action, figure 4" /></a>

	Measure the component down the slope

	Component down the slope = 3kN

	<dl>
		<dt>A man pushes a car with a force of 550N for 12m. How much work was done?</dt>
		<dd id="Resolving-Forces0" class="js-click-to-reveal">Your answer should include: 6600J / 6600 Explanation: 6600J</dd>
		<dt>A child pulled a toy train across a room with a force of 6N. The child pulls the toy a distance of 4m. How much work does the child do?</dt>
		<dd id="Resolving-Forces1" class="js-click-to-reveal">Your answer should include: 24J / 24 Explanation: 24J</dd>
		<dt>A pupil investigates Hooke’s law for a spring. When a mass of 100g is hung on the spring, the total length of the spring is 12cm. When a 300g mass is hung on it, the total length of the spring is 16cm. How long will the spring be when 200g is hung on it?</dt>
		<dd id="Resolving-Forces2" class="js-click-to-reveal">Your answer should include: 14cm / 14 Explanation: 14cm</dd>
		<dt>What is the unstretched length of the spring in the previous question?</dt>
		<dd id="Resolving-Forces3" class="js-click-to-reveal">Your answer should include: 10cm / 10 Explanation: 10cm</dd>
	</dl>
</main>

Forces in Action

<header>
			<h1 class="blog-post__title">Newton's Laws of Motion</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="newtons-laws-of-motion">Newton’s Laws of Motion</h2>

Forces can be categorised as contact or non-contact forces:

Contact Force - The objects are touching, i.e.:

<ol>
 <li>Friction</li>
 <li>Air resistance</li>
 <li>Tension</li>
</ol>

Non Contact Force - The objects are not touching, i.e.:

<ol>
 <li>Gravity</li>
 <li>Magnetism</li>
 <li>Electromagnetism</li>
</ol>

<h2 id="newtons-3rd-law-of-motion">Newton’s 3rd Law of Motion</h2>

Every action has an equal and opposite reaction

For example, if you push against a wall, the wall must be producing an equal and opposite force on you otherwise the wall would fall over or your hand would go through the wall.

<img src="/img/notes/02/3rd-law-1.png" alt="Newton's Laws of Motion, figure 1" /></a>

Gravity is pulling you down towards the centre of the earth but, at this moment you are (probably) not moving down through the floor. This is because the floor exerts an equal and opposite force on you, holding you up.

<img src="/img/notes/02/3rd-law-2.png" alt="Newton's Laws of Motion, figure 2" /></a>

Other examples include:

The recoil force on a gun (the gun recoils back to the shooter as the bullet is fired)

<img src="/img/notes/02/recoil.png" alt="Newton's Laws of Motion, figure 3" /></a>

Exhaust gases used to provide thrust for a rocket

<img src="/img/notes/02/rocket.png" alt="Newton's Laws of Motion, figure 4" /></a>

Jet engines

<img src="/img/notes/02/jet.png" alt="Newton's Laws of Motion, figure 5" /></a>

Car tyres

<img src="/img/notes/02/driving.png" alt="Newton's Laws of Motion, figure 6" /></a>

If a car is driving on softer ground, such as mud, the wheel still exerts a force on mud backwards. However, the mud is unable to produce a reaction force to push the car forwards. Therefore the wheels spin and spray mud backwards but the car does not move forwards.

<img src="/img/notes/02/mud.png" alt="Newton's Laws of Motion, figure 7" /></a>

<h2 id="newtons-1st-law-of-motion">Newton’s 1st Law of Motion</h2>

On any object, there are usually multiple forces acting.

<img src="/img/notes/02/car.png" alt="Newton's Laws of Motion, figure 1" /></a>

The resultant force is the sum of all the forces acting on an object.

<img src="/img/notes/02/resultant.png" alt="Newton's Laws of Motion, figure 2" /></a>

Newton’s 1st law of motion states that an object will stay at rest, or continue at a constant speed, unless it is acted on by an unbalanced force.

This means:

<ol>
 <li>Balanced forces = no change in motion (this could mean the object is not moving OR that it is moving at a constant speed)</li>
 <li>Unbalanced forces = change in motion (this could be speeding up, slowing down or changing direction)</li>
</ol>

For example, the reason you are thrown forwards in a head-on collision is that objects continue in their current state (rest or constant speed) unless acted on by a resultant force. Therefore, your body will continue moving forwards until it experiences a force slowing it down (eg from the road ahead).

<img src="/img/notes/02/inertia.png" alt="Newton's Laws of Motion, figure 3" /></a>

If an astronaut throws an object in space it will continue moving at a constant speed because there is no air resistance to slow it down. If you throw the same object on the Earth, air resistance slows it down and gravity pulls it to the ground where it then experiences friction, bringing it to a stop.

<h2 id="gravity">Gravity</h2>

<ol>
 <li>Mass - The amount of matter in an object. Measured in kilograms (kg)</li>
 <li>Weight - The force on an object due to gravity. Measured in Newtons (N)</li>
 <li>Gravity – The force of attraction between objects</li>
</ol>

For example, the mass of an astronaut is the same whether on the Earth, the moon or in outer space because there is the same amount of matter in the body of the astronaut. However, his weight is different in those locations because of the different gravitational field strength.

<img src="/img/notes/02/gravity.png" alt="Newton's Laws of Motion, figure 1" /></a>

The relationship between mass, weight and gravity is described in this equation (you DO need to remember this for your exam):

<h2 class="ql-align-center">W = mg</h2>

W = weight (N)

m = mass (kg)

g = gravity (N/kg)

<h2 id="newtons-2nd-law-of-motion">Newton’s 2nd Law of Motion</h2>

Newton’s 2nd law applies to objects that have a resultant force acting on them (and so their motion is changing)

The acceleration of an object is directly proportional to the force acting on it, and inversely proportional to it’s mass.

<ol>
 <li>Bigger force = bigger acceleration</li>
 <li>Bigger mass = smaller acceleration</li>
</ol>

For example, if the same force is applied to these vehicles, the motorbike will accelerate faster due to its smaller mass.

<img src="/img/notes/02/law2-1.png" alt="Newton's Laws of Motion, figure 1" /></a>

Or, to achieve equal acceleration a greater force will be needed for the truck due to its larger mass.

<img src="/img/notes/02/law-2-2.png" alt="Newton's Laws of Motion, figure 2" /></a>

Newton’s 2nd law is often represented by an equation (you DO need to remember this equation in your exam).

<h2 class="ql-align-center">F = ma</h2>

F = force (N)

__m __= mass (kg)

a = acceleration (m/s2)

Worked Example

Calculate the resultant force on an object of mass 6kg when it has an acceleration of 3m/s2

<ol>
 <li>F = ma</li>
 <li>F = 6 x 3</li>
 <li>F = 18N</li>
</ol>

<dl>
	<dt>A car accelerates forwards. What direction is the force that the car exerts on the driver?</dt>
	<dd id="Newtons-2nd-Law-of-Motion0" class="js-click-to-reveal">forwards</dd>
	<dt>A car accelerates forwards. What direction is the force that the driver exerts on the car?</dt>
	<dd id="Newtons-2nd-Law-of-Motion1" class="js-click-to-reveal">backwards</dd>
	<dt>What force is required to accelerate an object of 3kg at 2m/s2?</dt>
	<dd id="Newtons-2nd-Law-of-Motion2" class="js-click-to-reveal">Your answer should include: 6N / 6</dd>
	<dt>What is the weight of an object of mass 15kg on the Earth (gravitational field strength 9.81 N/kg)?</dt>
	<dd id="Newtons-2nd-Law-of-Motion3" class="js-click-to-reveal">Your answer should include: 147.15N / 147.15</dd>
	<dt>What is the mass of an object that weighs 70N on the moon, where the gravitational field strength is 1.6N/kg?</dt>
	<dd id="Newtons-2nd-Law-of-Motion4" class="js-click-to-reveal">Your answer should include: 43.75kg / 43.75</dd>
</dl>

<h2 id="terminal-velocity">Terminal Velocity</h2>

As an object falls, it’s speed changes due to the changing forces acting on it.

At first the weight is greater than the air resistance and so the sky-diver speeds up.

<img src="/img/notes/02/tv1.png" alt="Newton's Laws of Motion, figure 1" /></a>

The faster the sky-diver gets, the bigger the force of air resistance becomes because there are more collisions with air particles (the weight remains constant throughout the fall)

<img src="/img/notes/02/tv2.png" alt="Newton's Laws of Motion, figure 2" /></a>

Eventually, the air resistance equals the weight. The forces are now balanced so the sky diver continues falling at a constant speed. This maximum speed is known as terminal velocity.

<img src="/img/notes/02/tv3.png" alt="Newton's Laws of Motion, figure 3" /></a>

When the sky-diver opens the parachute, the air resistance increases dramatically and is greater than the weight. This unbalanced force slows the sky-diver down.

<img src="/img/notes/02/tv4.png" alt="Newton's Laws of Motion, figure 4" /></a>

As the sky-diver slows down, the air resistance decreases as there are less collisions with air particles taking place. Eventually, the air resistance equals the weight again and the forces are balanced. The sky-diver will continue at a constant speed (which is a lower speed than before the parachute is opened).

<img src="/img/notes/02/tv5.png" alt="Newton's Laws of Motion, figure 5" /></a>

		</main>

<header>
			<h1 class="blog-post__title">Newton's Laws of Motion</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="newtons-laws-of-motion">Newton’s Laws of Motion</h2>

Forces can be categorized as contact or non-contact forces:

Contact Force - The objects are touching, i.e.:

<ol>
 <li>Friction</li>
 <li>Air resistance</li>
 <li>Tension</li>
</ol>

Non-Contact Force - The objects are not touching, i.e.:

<ol>
 <li>Gravity</li>
 <li>Magnetism</li>
 <li>Electromagnetism</li>
</ol>

<h2 id="newtons-3rd-law-of-motion">Newton’s 3rd Law of Motion</h2>

Every action has an equal and opposite reaction.

For example, if you push against a wall, the wall must be producing an equal and opposite force on you; otherwise, the wall would fall over or your hand would go through the wall.

<img src="/img/notes/02/3rd-law-1.png" alt="Newton's Laws of Motion, figure 1" />

Gravity is pulling you down towards the center of the earth, but at this moment, you are (probably) not moving down through the floor. This is because the floor exerts an equal and opposite force on you, holding you up.

<img src="/img/notes/02/3rd-law-2.png" alt="Newton's Laws of Motion, figure 2" />

Other examples include:

The recoil force on a gun (the gun recoils back to the shooter as the bullet is fired)

<img src="/img/notes/02/recoil.png" alt="Newton's Laws of Motion, figure 3" />

Exhaust gases used to provide thrust for a rocket

<img src="/img/notes/02/rocket.png" alt="Newton's Laws of Motion, figure 4" />

Jet engines

<img src="/img/notes/02/jet.png" alt="Newton's Laws of Motion, figure 5" />

Car tires

<img src="/img/notes/02/driving.png" alt="Newton's Laws of Motion, figure 6" />

If a car is driving on softer ground, such as mud, the wheel still exerts a force on the mud backwards. However, the mud is unable to produce a reaction force to push the car forwards. Therefore, the wheels spin and spray mud backwards, but the car does not move forwards.

<img src="/img/notes/02/mud.png" alt="Newton's Laws of Motion, figure 7" />

<h2 id="newtons-1st-law-of-motion">Newton’s 1st Law of Motion</h2>

On any object, there are usually multiple forces acting.

<img src="/img/notes/02/car.png" alt="Newton's Laws of Motion, figure 1" />

The resultant force is the sum of all the forces acting on an object.

<img src="/img/notes/02/resultant.png" alt="Newton's Laws of Motion, figure 2" />

Newton’s 1st law of motion states that an object will stay at rest or continue at a constant speed unless it is acted on by an unbalanced force.

This means:

<ol>
 <li>Balanced forces = no change in motion (this could mean the object is not moving OR that it is moving at a constant speed)</li>
 <li>Unbalanced forces = change in motion (this could be speeding up, slowing down, or changing direction)</li>
</ol>

For example, the reason you are thrown forwards in a head-on collision is that objects continue in their current state (rest or constant speed) unless acted on by a resultant force. Therefore, your body will continue moving forwards until it experiences a force slowing it down (e.g., from the road ahead).

<img src="/img/notes/02/inertia.png" alt="Newton's Laws of Motion, figure 3" />

If an astronaut throws an object in space, it will continue moving at a constant speed because there is no air resistance to slow it down. If you throw the same object on Earth, air resistance slows it down and gravity pulls it to the ground where it then experiences friction, bringing it to a stop.

<h2 id="gravity">Gravity</h2>

<ol>
 <li>Mass - The amount of matter in an object. Measured in kilograms (kg)</li>
 <li>Weight - The force on an object due to gravity. Measured in Newtons (N)</li>
 <li>Gravity – The force of attraction between objects</li>
</ol>

For example, the mass of an astronaut is the same whether on Earth, the moon, or in outer space because there is the same amount of matter in the body of the astronaut. However, his weight is different in those locations because of the different gravitational field strength.

<img src="/img/notes/02/gravity.png" alt="Newton's Laws of Motion, figure 1" />

The relationship between mass, weight, and gravity is described in this equation (you DO need to remember this for your exam):

<h2 class="ql-align-center">W = mg</h2>

W = weight (N)

m = mass (kg)

g = gravity (N/kg)

<h2 id="newtons-2nd-law-of-motion">Newton’s 2nd Law of Motion</h2>

Newton’s 2nd law applies to objects that have a resultant force acting on them (and so their motion is changing).

The acceleration of an object is directly proportional to the force acting on it and inversely proportional to its mass.

<ol>
 <li>Bigger force = bigger acceleration</li>
 <li>Bigger mass = smaller acceleration</li>
</ol>

For example, if the same force is applied to these vehicles, the motorbike will accelerate faster due to its smaller mass.

<img src="/img/notes/02/law2-1.png" alt="Newton's Laws of Motion, figure 1" />

Or, to achieve equal acceleration, a greater force will be needed for the truck due to its larger mass.

<img src="/img/notes/02/law-2-2.png" alt="Newton's Laws of Motion, figure 2" />

Newton’s 2nd law is often represented by an equation (you DO need to remember this equation in your exam).

<h2 class="ql-align-center">F = ma</h2>

F = force (N)

m = mass (kg)

a = acceleration (m/s2)

Worked Example

Calculate the resultant force on an object of mass 6kg when it has an acceleration of 3m/s2

<ol>
 <li>F = ma</li>
 <li>F = 6 x 3</li>
 <li>F = 18N</li>
</ol>

<dl>
	<dt>A car accelerates forwards. What direction is the force that the car exerts on the driver?</dt>
	<dd id="Newtons-2nd-Law-of-Motion0" class="js-click-to-reveal">Forwards</dd>
	<dt>A car accelerates forwards. What direction is the force that the driver exerts on the car?</dt>
	<dd id="Newtons-2nd-Law-of-Motion1" class="js-click-to-reveal">Backwards</dd>
	<dt>What force is required to accelerate an object of 3kg at 2m/s2?</dt>
	<dd id="Newtons-2nd-Law-of-Motion2" class="js-click-to-reveal">Your answer should include: 6N / 6</dd>
	<dt>What is the weight of an object of mass 15kg on Earth (gravitational field strength 9.81 N/kg)?</dt>
	<dd id="Newtons-2nd-Law-of-Motion3" class="js-click-to-reveal">Your answer should include: 147.15N / 147.15</dd>
	<dt>What is the mass of an object that weighs 70N on the moon, where the gravitational field strength is 1.6N/kg?</dt>
	<dd id="Newtons-2nd-Law-of-Motion4" class="js-click-to-reveal">Your answer should include: 43.75kg / 43.75</dd>
</dl>

<h2 id="terminal-velocity">Terminal Velocity</h2>

As an object falls, its speed changes due to the changing forces acting on it.

At first, the weight is greater than the air resistance, so the skydiver speeds up.

<img src="/img/notes/02/tv1.png" alt="Newton's Laws of Motion, figure 1" />

The faster the skydiver gets, the bigger the force of air resistance becomes because there are more collisions with air particles (the weight remains constant throughout the fall).

<img src="/img/notes/02/tv2.png" alt="Newton's Laws of Motion, figure 2" />

Eventually, the air resistance equals the weight. The forces are now balanced, so the skydiver continues falling at a constant speed. This maximum speed is known as terminal velocity.

<img src="/img/notes/02/tv3.png" alt="Newton's Laws of Motion, figure 3" />

When the skydiver opens the parachute, the air resistance increases dramatically and is greater than the weight. This unbalanced force slows the skydiver down.

<img src="/img/notes/02/tv4.png" alt="Newton's Laws of Motion, figure 4" />

As the skydiver slows down, the air resistance decreases as there are fewer collisions with air particles taking place. Eventually, the air resistance equals the weight again, and the forces are balanced. The skydiver will continue at a constant speed (which is a lower speed than before the parachute is opened).

<img src="/img/notes/02/tv5.png" alt="Newton's Laws of Motion, figure 5" />

		</main>

Newton's Laws of Motion

<header>
			<h1 class="blog-post__title">Transverse and Longitudinal Waves</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="waves">Waves</h2>

Waves transfer energy but not matter (the particles vibrate to pass energy on, but do not change their overall position.

There are two types of waves:

<ol>
 <li>Longitudinal</li>
 <li>Transverse</li>
</ol>

<img src="/img/notes/02/waves.gif" alt="Transverse and Longitudinal Waves, figure 1" /></a>

<h2 id="transverse-waves">Transverse Waves</h2>

Vibrations are at right angles to the motion of the wave. Examples of transverse waves include light, water, and mexican waves!

<img src="/img/notes/02/transversegif.gif" alt="Transverse and Longitudinal Waves, figure 1" /></a>

Transverse waves have peaks/crests and troughs. The amplitude of the wave is the distance from the central point to a peak or a trough (the maximum displacement of the wave). The wavelength of the wave (given the symbol λ) is the distance from one peak to the next or from one trough to the next.

<img src="/img/notes/02/transverse.png" alt="Transverse and Longitudinal Waves, figure 2" /></a>

<h2 id="required-practical--measuring-waves">Required Practical – Measuring Waves</h2>

Wave features can be measured using a ripple tank. A motor produces waves (ripples) in a shallow tank of water. The tank has a transparent base and a light above it. This allows the waves to be seen as shadows moving on the surface below the tank.

<img src="/img/notes/02/ripple-tank.png" alt="Transverse and Longitudinal Waves, figure 1" /></a>

The wavelength is the distance between two shadows and the frequency is the number of shadows passing a point each second. This can be difficult to do as the waves/shadows are moving constantly.

Video Ripple tank 1</a>

Video Ripple tank 2</a>

Standing waves can be produced using a piece of string/elastic attached to a vibration generator. As the frequency of the vibrations is adjusted, a standing (stationary) wave can be produced.

<img src="/img/notes/02/standing-waves.png" alt="Transverse and Longitudinal Waves, figure 2" /></a>

The wavelength is the distance across two nodes. The frequency can be measured from the vibration generator itself.

Video Standing Waves 1</a>

Video Standing Waves 2</a>

<h2 id="required-practical--reflection">Required Practical – Reflection</h2>

Reflection from a plane (flat) mirror can be investigated by using a ray box to shine a single ray of light at the mirror. If the mirror and ray box are set up on top of a piece of paper, the position of the mirror, the incident ray (the ray of light travelling from the ray box to the mirror) and the reflected ray (the ray of light that has reflected off the mirror) can be marked on the paper.

<img src="/img/notes/02/reflection-1024x818.jpg" alt="Transverse and Longitudinal Waves, figure 1" /></a>

With these light rays drawn, a line should be drawn at 90o to the mirror at the position where the ray was reflected. This is called the ‘normal’. The angle of incidence and angle of reflection can then be measured by using a protractor to measure the angle between the ray and the normal.

<img src="/img/notes/02/Reflection122.jpeg" alt="Transverse and Longitudinal Waves, figure 2" /></a>

The law of reflection states that the angle of incidence is always equal to the angle of reflection.

Video 1</a>

Video 2</a>

<h2 id="required-practical--refraction">Required Practical – Refraction</h2>

The movement of light from one medium (material) to another can be investigated by using a ray box to shine a single ray of through a glass or Perspex block. If the block and ray box are set up on top of a piece of paper, the position of the block and the light rays entering and leaving the block can be marked on the paper.

<img src="/img/notes/02/Refraction_photo-1024x681.png" alt="Transverse and Longitudinal Waves, figure 1" /></a>

If the ray of light enters the block at 90o to the edge of the block, it will pass through the block without changing direction. If the ray enters the block at an angle, it’s path will bend towards the normal as it enters the block and away from the normal when it leaves the block. This is known as refraction and occurs because the light changes speed as it travels from one material to another. (this will be explained in the light lesson)

<img src="/img/notes/02/refraction-1024x466.jpg" alt="Transverse and Longitudinal Waves, figure 2" /></a>

Video 1</a>

Video 2</a>

<h2 id="longitudinal-waves">Longitudinal Waves</h2>

Vibrations are in the same direction as the motion of the wave. Sound is an example of a longitudinal wave.

<img src="/img/notes/02/longitudinalgif.gif" alt="Transverse and Longitudinal Waves, figure 1" /></a>

Longitudinal waves have compressions (areas where the particles are closer together) and rarefactions (areas where particles are further apart). The wavelength of a longitudinal wave is the distance from one compression to the next.

<img src="/img/notes/02/longitudinal.png" alt="Transverse and Longitudinal Waves, figure 2" /></a>

Frequency

The frequency of a wave is the number of waves passing a point in 1 second. Frequency is measured in Hertz (Hz).

A wave with a high frequency will have a short wavelength and a low frequency wave will have a long wavelength (provided the speed of the wave is constant).

Period

The period of a wave is the time take for one complete oscillation.

Period = 1 ÷ frequency

Wave Speed

Wave speed is calculated using this equation (you DO need to remember this equation for your exam):

<h2 class="ql-align-center">v = f λ</h2>

v = wavespeed (m/s)

__f __= frequency (Hz)

λ = wavelength (m)

<h2 id="sound">Sound</h2>

Sound waves are longitudinal waves that travel through the air from a vibrating object to our ears.

In the ear, the sound wave causes the ear drum to vibrate. These vibrations are converted to an electrical signal which travels to the brain.

The bigger the amplitude of the wave, the louder the sound. The shorter the wavelength of the wave, the higher pitched the sound. High frequency = high pitch.

<img src="/img/notes/02/sound.png" alt="Transverse and Longitudinal Waves, figure 1" /></a>

The conversion from sound waves to vibrations in a solid (eg the ear drum) only works efficiently over a limited range. Therefore, the range of human hearing is limited

Human hearing range is approximately 20Hz – 20kHz.

<img src="/img/notes/02/hearing-range-1024x656.png" alt="Transverse and Longitudinal Waves, figure 2" /></a>

Different animals have different hearing ranges:

<img src="/img/notes/02/Animal_hearing_frequency_range.svg.png" alt="Transverse and Longitudinal Waves, figure 3" /></a>

<h2 id="ultrasound">Ultrasound</h2>

Sound waves travel at different speeds through different materials. Materials reflect/absorb sound in different ways. These differences can be used to build up a picture of structures which would not normally be visible

Ultrasound is sound above the hearing range of humans (20kHz)

Ultrasound can be used to create an image of a baby in the womb or of other structures in the human body.

<img src="/img/notes/02/ultrasound.png" alt="Transverse and Longitudinal Waves, figure 1" /></a>

Ultrasound travels into the body and some is reflected at the boundary of different tissues

The reflected ultrasound arriving back at the detector at different times can build up a picture of the depth of the different tissues

<img src="/img/notes/02/ultrasound2.png" alt="Transverse and Longitudinal Waves, figure 2" /></a>

Advantages of using ultrasound

<ol>
 <li>They can be used to scan organs and other soft tissues (which are not dense enough to absorb X-rays)</li>
 <li>Ultrasound is non-ionising so there is no risk to the cells in the body</li>
</ol>

<img src="/img/notes/02/ultrasound.gif" alt="Transverse and Longitudinal Waves, figure 3" /></a>

<h2 id="echo-sounding">Echo Sounding</h2>

Echo sounding uses pulses of high-frequency sound to measure the depth of water or to detect objects in deep water

The time taken for the reflected sound to arrive back at the detector is used to calculate depth

<img src="/img/notes/02/echo-sounding.gif" alt="Transverse and Longitudinal Waves, figure 1" /></a>

<h2 id="seismic-waves">Seismic Waves</h2>

The Earth’s structure can be described as 4 parts: the crust, the mantle (molten rock), a liquid outer core and a solid inner core.

<img src="/img/notes/02/structure.png" alt="Transverse and Longitudinal Waves, figure 1" /></a>

This model for the structure of the Earth has been developed using seismic waves – the shock waves produced by earthquakes. There are two main types of seismic waves, P-waves (primary waves) and S-waves (secondary waves)

P-Waves

<ol>
 <li>Primary (travel faster, arrive first)</li>
 <li>Longitudinal Waves</li>
 <li>Can travel through solid and liquid (core)</li>
 <li>Cause a one-off ‘impact’</li>
</ol>

<img src="/img/notes/02/pwave.gif" alt="Transverse and Longitudinal Waves, figure 2" /></a>

S-Waves

<ol>
 <li>Secondary (travel slower, arrive second)</li>
 <li>Transverse Waves</li>
 <li>Can not travel through liquid (core)</li>
 <li>Cause shaking</li>
</ol>

<img src="/img/notes/02/swaves.gif" alt="Transverse and Longitudinal Waves, figure 3" /></a>

Seismic waves travel through the earth after an earthquake. The longer the gap between detecting the P and S waves, the further away the epicentre of the earthquake is

<img src="/img/notes/02/seismograph.png" alt="Transverse and Longitudinal Waves, figure 4" /></a>

<dl>
	<dt>Which type of wave has vibrations in the same direction as the motion of the wave?</dt>
	<dd id="Seismic-Waves0" class="js-click-to-reveal">longitudinal</dd>
	<dt>Which type of wave has vibrations at right angles to the motion of the wave?</dt>
	<dd id="Seismic-Waves1" class="js-click-to-reveal">transverse</dd>
	<dt>What is the name of the maximum displacement of a wave (distance to peak or trough)?</dt>
	<dd id="Seismic-Waves2" class="js-click-to-reveal">amplitude</dd>
	<dt>What is the name of the distance from one peak to the next?</dt>
	<dd id="Seismic-Waves3" class="js-click-to-reveal">wavelength</dd>
	<dt>What units is frequency measured in?</dt>
	<dd id="Seismic-Waves4" class="js-click-to-reveal">Your answer should include: Hertz / Hz</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Transverse and Longitudinal Waves</h1>
</header>

<main class="blog-post__content">
	<h2 id="waves">Waves</h2>

	Waves transfer energy but not matter. The particles vibrate to pass energy on, but do not change their overall position.

	There are two types of waves:

	<ol>
		<li>Longitudinal</li>
		<li>Transverse</li>
	</ol>

	<a href="/img/notes/02/waves.gif" target="_blank"><img src="/img/notes/02/waves.gif" alt="Transverse and Longitudinal Waves, figure 1" /></a>

	<h2 id="transverse-waves">Transverse Waves</h2>

	Vibrations are at right angles to the motion of the wave. Examples of transverse waves include light, water, and Mexican waves!

	<a href="/img/notes/02/transversegif.gif" target="_blank"><img src="/img/notes/02/transversegif.gif" alt="Transverse and Longitudinal Waves, figure 1" /></a>

	Transverse waves have peaks/crests and troughs. The amplitude of the wave is the distance from the central point to a peak or a trough (the maximum displacement of the wave). The wavelength of the wave (given the symbol λ) is the distance from one peak to the next or from one trough to the next.

	<a href="/img/notes/02/transverse.png" target="_blank"><img src="/img/notes/02/transverse.png" alt="Transverse and Longitudinal Waves, figure 2" /></a>

	<h2 id="required-practical--measuring-waves">Required Practical – Measuring Waves</h2>

	Wave features can be measured using a ripple tank. A motor produces waves (ripples) in a shallow tank of water. The tank has a transparent base and a light above it. This allows the waves to be seen as shadows moving on the surface below the tank.

	<a href="/img/notes/02/ripple-tank.png" target="_blank"><img src="/img/notes/02/ripple-tank.png" alt="Transverse and Longitudinal Waves, figure 1" /></a>

	The wavelength is the distance between two shadows and the frequency is the number of shadows passing a point each second. This can be difficult to do as the waves/shadows are moving constantly.

	Standing waves can be produced using a piece of string/elastic attached to a vibration generator. As the frequency of the vibrations is adjusted, a standing (stationary) wave can be produced.

	<a href="/img/notes/02/standing-waves.png" target="_blank"><img src="/img/notes/02/standing-waves.png" alt="Transverse and Longitudinal Waves, figure 2" /></a>

	The wavelength is the distance across two nodes. The frequency can be measured from the vibration generator itself.

	<h2 id="required-practical--reflection">Required Practical – Reflection</h2>

	Reflection from a plane (flat) mirror can be investigated by using a ray box to shine a single ray of light at the mirror. If the mirror and ray box are set up on top of a piece of paper, the position of the mirror, the incident ray (the ray of light traveling from the ray box to the mirror), and the reflected ray (the ray of light that has reflected off the mirror) can be marked on the paper.

	<a href="/img/notes/02/reflection-1024x818.jpg" target="_blank"><img src="/img/notes/02/reflection-1024x818.jpg" alt="Transverse and Longitudinal Waves, figure 1" /></a>

	With these light rays drawn, a line should be drawn at 90o to the mirror at the position where the ray was reflected. This is called the ‘normal’. The angle of incidence and angle of reflection can then be measured by using a protractor to measure the angle between the ray and the normal.

	<a href="/img/notes/02/Reflection122.jpeg" target="_blank"><img src="/img/notes/02/Reflection122.jpeg" alt="Transverse and Longitudinal Waves, figure 2" /></a>

	The law of reflection states that the angle of incidence is always equal to the angle of reflection.

	<h2 id="required-practical--refraction">Required Practical – Refraction</h2>

	The movement of light from one medium (material) to another can be investigated by using a ray box to shine a single ray of light through a glass or Perspex block. If the block and ray box are set up on top of a piece of paper, the position of the block and the light rays entering and leaving the block can be marked on the paper.

	<a href="/img/notes/02/Refraction_photo-1024x681.png" target="_blank"><img src="/img/notes/02/Refraction_photo-1024x681.png" alt="Transverse and Longitudinal Waves, figure 1" /></a>

	If the ray of light enters the block at 90o to the edge of the block, it will pass through the block without changing direction. If the ray enters the block at an angle, its path will bend towards the normal as it enters the block and away from the normal when it leaves the block. This is known as refraction and occurs because the light changes speed as it travels from one material to another. (This will be explained in the light lesson)

	<a href="/img/notes/02/refraction-1024x466.jpg" target="_blank"><img src="/img/notes/02/refraction-1024x466.jpg" alt="Transverse and Longitudinal Waves, figure 2" /></a>

	<h2 id="longitudinal-waves">Longitudinal Waves</h2>

	Vibrations are in the same direction as the motion of the wave. Sound is an example of a longitudinal wave.

	<a href="/img/notes/02/longitudinalgif.gif" target="_blank"><img src="/img/notes/02/longitudinalgif.gif" alt="Transverse and Longitudinal Waves, figure 1" /></a>

	Longitudinal waves have compressions (areas where the particles are closer together) and rarefactions (areas where particles are further apart). The wavelength of a longitudinal wave is the distance from one compression to the next.

	<a href="/img/notes/02/longitudinal.png" target="_blank"><img src="/img/notes/02/longitudinal.png" alt="Transverse and Longitudinal Waves, figure 2" /></a>

	Frequency

	The frequency of a wave is the number of waves passing a point in 1 second. Frequency is measured in Hertz (Hz).

	A wave with a high frequency will have a short wavelength and a low frequency wave will have a long wavelength (provided the speed of the wave is constant).

	Period

	The period of a wave is the time taken for one complete oscillation.

	Period = 1 ÷ frequency

	Wave Speed

	Wave speed is calculated using this equation (you DO need to remember this equation for your exam):

	<h2 class="ql-align-center">v = f λ</h2>

	v = wave speed (m/s)

	f = frequency (Hz)

	λ = wavelength (m)

	<h2 id="sound">Sound</h2>

	Sound waves are longitudinal waves that travel through the air from a vibrating object to our ears.

	In the ear, the sound wave causes the eardrum to vibrate. These vibrations are converted to an electrical signal which travels to the brain.

	The bigger the amplitude of the wave, the louder the sound. The shorter the wavelength of the wave, the higher pitched the sound. High frequency = high pitch.

	<a href="/img/notes/02/sound.png" target="_blank"><img src="/img/notes/02/sound.png" alt="Transverse and Longitudinal Waves, figure 1" /></a>

	The conversion from sound waves to vibrations in a solid (e.g. the eardrum) only works efficiently over a limited range. Therefore, the range of human hearing is limited.

	Human hearing range is approximately 20Hz – 20kHz.

	<a href="/img/notes/02/hearing-range-1024x656.png" target="_blank"><img src="/img/notes/02/hearing-range-1024x656.png" alt="Transverse and Longitudinal Waves, figure 2" /></a>

	Different animals have different hearing ranges:

	<a href="/img/notes/02/Animal_hearing_frequency_range.svg.png" target="_blank"><img src="/img/notes/02/Animal_hearing_frequency_range.svg.png" alt="Transverse and Longitudinal Waves, figure 3" /></a>

	<h2 id="ultrasound">Ultrasound</h2>

	Sound waves travel at different speeds through different materials. Materials reflect/absorb sound in different ways. These differences can be used to build up a picture of structures which would not normally be visible.

	Ultrasound is sound above the hearing range of humans (20kHz).

	Ultrasound can be used to create an image of a baby in the womb or of other structures in the human body.

	<a href="/img/notes/02/ultrasound.png" target="_blank"><img src="/img/notes/02/ultrasound.png" alt="Transverse and Longitudinal Waves, figure 1" /></a>

	Ultrasound travels into the body and some is reflected at the boundary of different tissues.

	The reflected ultrasound arriving back at the detector at different times can build up a picture of the depth of the different tissues.

	<a href="/img/notes/02/ultrasound2.png" target="_blank"><img src="/img/notes/02/ultrasound2.png" alt="Transverse and Longitudinal Waves, figure 2" /></a>

	Advantages of using ultrasound

	<ol>
		<li>They can be used to scan organs and other soft tissues (which are not dense enough to absorb X-rays).</li>
		<li>Ultrasound is non-ionizing so there is no risk to the cells in the body.</li>
	</ol>

	<a href="/img/notes/02/ultrasound.gif" target="_blank"><img src="/img/notes/02/ultrasound.gif" alt="Transverse and Longitudinal Waves, figure 3" /></a>

	<h2 id="echo-sounding">Echo Sounding</h2>

	Echo sounding uses pulses of high-frequency sound to measure the depth of water or to detect objects in deep water.

	The time taken for the reflected sound to arrive back at the detector is used to calculate depth.

	<a href="/img/notes/02/echo-sounding.gif" target="_blank"><img src="/img/notes/02/echo-sounding.gif" alt="Transverse and Longitudinal Waves, figure 1" /></a>

	<h2 id="seismic-waves">Seismic Waves</h2>

	The Earth’s structure can be described as 4 parts: the crust, the mantle (molten rock), a liquid outer core, and a solid inner core.

	<a href="/img/notes/02/structure.png" target="_blank"><img src="/img/notes/02/structure.png" alt="Transverse and Longitudinal Waves, figure 1" /></a>

	This model for the structure of the Earth has been developed using seismic waves – the shock waves produced by earthquakes. There are two main types of seismic waves, P-waves (primary waves) and S-waves (secondary waves).

	P-Waves

	<ol>
		<li>Primary (travel faster, arrive first)</li>
		<li>Longitudinal Waves</li>
		<li>Can travel through solid and liquid (core)</li>
		<li>Cause a one-off ‘impact’</li>
	</ol>

	<a href="/img/notes/02/pwave.gif" target="_blank"><img class="img-30" src="/img/notes/02/pwave.gif" alt="Transverse and Longitudinal Waves, figure 2" /></a>

	S-Waves

	<ol>
		<li>Secondary (travel slower, arrive second)</li>
		<li>Transverse Waves</li>
		<li>Cannot travel through liquid (core)</li>
		<li>Cause shaking</li>
	</ol>

	<a href="/img/notes/02/swaves.gif" target="_blank"><img class="img-30" src="/img/notes/02/swaves.gif" alt="Transverse and Longitudinal Waves, figure 3" /></a>

	Seismic waves travel through the earth after an earthquake. The longer the gap between detecting the P and S waves, the further away the epicenter of the earthquake is.

	<a href="/img/notes/02/seismograph.png" target="_blank"><img src="/img/notes/02/seismograph.png" alt="Transverse and Longitudinal Waves, figure 4" /></a>

	<dl>
		<dt>Which type of wave has vibrations in the same direction as the motion of the wave?</dt>
		<dd id="Seismic-Waves0" class="js-click-to-reveal">longitudinal</dd>
		<dt>Which type of wave has vibrations at right angles to the motion of the wave?</dt>
		<dd id="Seismic-Waves1" class="js-click-to-reveal">transverse</dd>
		<dt>What is the name of the maximum displacement of a wave (distance to peak or trough)?</dt>
		<dd id="Seismic-Waves2" class="js-click-to-reveal">amplitude</dd>
		<dt>What is the name of the distance from one peak to the next?</dt>
		<dd id="Seismic-Waves3" class="js-click-to-reveal">wavelength</dd>
		<dt>What units is frequency measured in?</dt>
		<dd id="Seismic-Waves4" class="js-click-to-reveal">Hertz (Hz)</dd>
	</dl>
</main>

Transverse and Longitudinal Waves

Waves

<header>
			<h1 class="blog-post__title">Light</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="reflection">Reflection</h2>

When light is reflected, the angle of incidence always equals the angle of reflection:

<img src="/img/notes/02/reflection-1024x487.gif" alt="Light, figure 1" /></a>

If the surface is smooth, then every ray of light is reflected at the same angle and a reflection can be seen (eg mirror). This is called specular reflection.

<img src="/img/notes/02/specular.png" alt="Light, figure 2" /></a>

If the surface is rough, then, although each ray of light obeys the law of reflection where it hits the surface, the rays of light do not all hit the surface at the same angle so they are not all reflected at the same angle as each other. This is called diffuse reflection, the object can be seen as some light will be reflected into the eye, but a reflected image can not be seen.

<img src="/img/notes/02/diffuse.png" alt="Light, figure 3" /></a>

Light travels as electromagnetic waves. Reflection of waves can be shown with a wave front diagram. The law of reflection still applies.

<img src="/img/notes/02/wavefront.png" alt="Light, figure 4" /></a>

To find the position of an image from a mirror, you need to construct a ray diagram with the angles drawn as accurately as you can. Draw 2 (or more) rays of light from your object to the mirror (at different angles). Draw the normal (line at 900 to mirror) for each ray and then measure the angle of incidence. Draw the reflected rays at the same angle using a protractor and then extend the reflected rays ‘behind’ the mirror. The place where there lines cross is the position of the image.

The image should be the same distance behind the mirror as the object is in front.

<img src="/img/notes/02/locating-image.png" alt="Light, figure 5" /></a>

<h2 id="light">Light</h2>

When light encounters a material, it could be transmitted (pass through), reflected, absorbed or scattered by the material:

<img src="/img/notes/02/transparant.png" alt="Light, figure 1" /></a>

<img src="/img/notes/02/translucent.png" alt="Light, figure 2" /></a>

<img src="/img/notes/02/opaque.png" alt="Light, figure 3" /></a>

<h2 id="refraction">Refraction</h2>

Refraction happens due to a change in speed. As light travels from one material to another, it changes speed

If the light enters parallel to the normal, the change in speed does not produce a noticeable effect. If the light enters at an angle, the change in speed results in a change in direction of the light.

<img src="/img/notes/02/refraction-gif.gif" alt="Light, figure 1" /></a>

As the wave front travels from one material to another at an angle, not all of the wave hits the boundary and changes speed at the same time. This causes the change in direction:

<img src="/img/notes/02/refraction-wavefronts.png" alt="Light, figure 2" /></a>

In the diagram, the refracted wave fronts are closer together than the incident wave fronts. The waves have the same frequency but travel at different speeds, so they have different __wavelengths __(v=fλ).

<h2 id="apparent-depth">Apparent Depth</h2>

If you are looking at an object that is under water, light is travelling from a source, reflecting off the object and travelling to your eye. As the light leaves the water, it is refracted. Your brain assumes that the light travelled in a straight line, so the object appears to be higher in the water than it actually is. The Archer fish takes this into account when it spits water at insects!

<img src="/img/notes/02/apparant-depth-1024x621.png" alt="Light, figure 1" /></a>

<h2 id="lenses">Lenses</h2>

A lens is a curved material that uses refraction of light to form an image. A convex (or converging) lens is thicker in the middle than the edges. A concave (or diverging) lens is thinner in the middle than the edges.

<img src="/img/notes/02/lenses.png" alt="Light, figure 1" /></a>

Convex (Converging) Lens

A convex lens causes parallel rays of light to converge to a point. The point where the rays meet is the focal point or principal focus. The distance from the centre of the lens to the focal point is the focal length.

<img src="/img/notes/02/cconvex.png" alt="Light, figure 2" /></a>

Concave (Diverging) Lens

A concave lens causes parallel rays of light to spread out (diverge). The point where the rays __appear to come from __is the focal point:

<img src="/img/notes/02/cconcave.png" alt="Light, figure 3" /></a>

Magnification = image height ÷ object height

<h2 id="constructing-ray-diagrams">Constructing Ray Diagrams</h2>

When drawing ray diagrams:

<ol>
 <li>Draw straight lines using a ruler</li>
 <li>Use arrows to show the direction</li>
 <li>Draw to scale</li>
 <li>Use correct symbols for convex and concave lenses:</li>
</ol>

<img src="/img/notes/02/lens-symbols.png" alt="Light, figure 1" /></a>

Draw 3 rays of light to construct your image:

1 - Parallel to axis – refracted through focal point

<img src="/img/notes/02/ray-diagrams-1.png" alt="Light, figure 2" /></a>

2 - Straight through the centre of the lens (not refracted)

<img src="/img/notes/02/ray-diagrams-2.png" alt="Light, figure 3" /></a>

3 - Through the focal point before the lens – refracted parallel to axis

<img src="/img/notes/02/ray-diagrams-3.png" alt="Light, figure 4" /></a>

<ol>
 <li>The image is produced where the 3 rays cross</li>
</ol>

<img src="/img/notes/02/ray-diagrams-4.png" alt="Light, figure 5" /></a>

Use the following words to describe images:

Real – the image could be formed on a screen (the rays of light actually meet at that point)

Virtual – the image could not be formed on a screen (the rays of light only appear to come from that point

Inverted – upside down

Upright – the same way up as the object

Diminished – smaller than the object

Magnified – larger than the object

Example ray diagrams:

<img src="/img/notes/02/convex-1.png" alt="Light, figure 6" /></a>

<img src="/img/notes/02/convex-2.png" alt="Light, figure 7" /></a>

<img src="/img/notes/02/concave.png" alt="Light, figure 8" /></a>

Worked Example

An object which is 5cm high is 8cm away from a convex lens of focal length 5cm. Construct a ray diagram to calculate the height of the image. Calculate the magnification of the lens.

<img src="/img/notes/02/lens-example.png" alt="Light, figure 9" /></a>

Image is:

<ol>
 <li>Real</li>
 <li>Inverted</li>
 <li>Magnified</li>
 <li>If diagram is drawn to scale, the image is approximately 8cm</li>
 <li>Magnification = 8÷ 5 = 1.6</li>
</ol>

<h2 id="colour">Colour</h2>

‘White’ light is made up of different colours called a spectrum. The colour of the light depends on the wavelength of that light. A prism can be used to separate white light into a spectrum as the different wavelengths (colours) are refracted by different amounts.

<img src="/img/notes/02/prism.gif" alt="Light, figure 1" /></a>

The colours of the spectrum are:

<ol>
 <li>Red</li>
 <li>Orange</li>
 <li>Yellow</li>
 <li>Green</li>
 <li>Blue</li>
 <li>Indigo</li>
 <li>Violet</li>
</ol>

Objects appear to be certain colours because they reflect some wavelengths of light and absorb others.

<ol>
 <li>White light (containing all colours) hits the red object</li>
 <li>Red light is reflected from the object</li>
 <li>All other colours are absorbed by the object</li>
 <li>The object appears red</li>
</ol>

<img src="/img/notes/02/red.png" alt="Light, figure 2" /></a>

<ol>
 <li>White light (containing all colours) hits the blue object</li>
 <li>Blue light is reflected from the object</li>
 <li>All other colours are absorbed by the object</li>
 <li>The object appears blue</li>
</ol>

<img src="/img/notes/02/blue.png" alt="Light, figure 3" /></a>

Other colours appear when different wavelengths are reflected in different amounts

<img src="/img/notes/02/other.png" alt="Light, figure 4" /></a>

A white object appears white because all wavelengths are reflected

<img src="/img/notes/02/white.png" alt="Light, figure 5" /></a>

A black object appears white because no light is reflected

<img src="/img/notes/02/black.png" alt="Light, figure 6" /></a>

<h2 id="coloured-lights">Coloured Lights</h2>

Objects can appear different colours under coloured lights. Under red light, a red object will still appear red as it will reflect red light. Under green light, the red object will appear black as the green light will be absorbed.

<img src="/img/notes/02/coloured-lights-1.png" alt="Light, figure 1" /></a>

A white object reflects all colours. Under red light, the white object will appear red. Under green light, the white object will appear green

<img src="/img/notes/02/coloured-lights-2.png" alt="Light, figure 2" /></a>

Video – a trick of the light</a>

<h2 id="colour-filters">Colour Filters</h2>

A colour filter absorbs some wavelengths of light and transmits others. A blue filter allows blue light to pass through but absorbs other colours

<img src="/img/notes/02/filters.png" alt="Light, figure 1" /></a>

<dl>
	<dt>What is the name of a lens which converges rays of light to a focal point?</dt>
	<dd id="Colour-Filters0" class="js-click-to-reveal">convex</dd>
	<dt>What is the name of a lens which diverges rays of light from a focal point?</dt>
	<dd id="Colour-Filters1" class="js-click-to-reveal">concave</dd>
	<dt>What colour will a yellow flag appear to be under red light?</dt>
	<dd id="Colour-Filters2" class="js-click-to-reveal">black</dd>
	<dt>What colour will a white flag appear to be under red light?</dt>
	<dd id="Colour-Filters3" class="js-click-to-reveal"> Explanation: red</dd>
	<dt>What is the name for the effect of light changing direction as it travels from one medium to another?</dt>
	<dd id="Colour-Filters4" class="js-click-to-reveal">refraction</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Light</h1>
</header>

<main class="blog-post__content">
	<h2 id="reflection">Reflection</h2>

	When light is reflected, the angle of incidence always equals the angle of reflection.

	<a href="/img/notes/02/reflection-1024x487.gif" target="_blank"><img src="/img/notes/02/reflection-1024x487.gif" alt="Light, figure 1" /></a>

	If the surface is smooth, then every ray of light is reflected at the same angle and a reflection can be seen (e.g. mirror). This is called specular reflection.

	<a href="/img/notes/02/specular.png" target="_blank"><img src="/img/notes/02/specular.png" alt="Light, figure 2" /></a>

	If the surface is rough, then, although each ray of light obeys the law of reflection where it hits the surface, the rays of light do not all hit the surface at the same angle so they are not all reflected at the same angle as each other. This is called diffuse reflection. The object can be seen as some light will be reflected into the eye, but a reflected image cannot be seen.

	<a href="/img/notes/02/diffuse.png" target="_blank"><img src="/img/notes/02/diffuse.png" alt="Light, figure 3" /></a>

	Light travels as electromagnetic waves. Reflection of waves can be shown with a wave front diagram. The law of reflection still applies.

	<a href="/img/notes/02/wavefront.png" target="_blank"><img src="/img/notes/02/wavefront.png" alt="Light, figure 4" /></a>

	To find the position of an image from a mirror, you need to construct a ray diagram with the angles drawn as accurately as you can. Draw 2 (or more) rays of light from your object to the mirror (at different angles). Draw the normal (line at 900 to mirror) for each ray and then measure the angle of incidence. Draw the reflected rays at the same angle using a protractor and then extend the reflected rays 'behind' the mirror. The place where these lines cross is the position of the image.

	The image should be the same distance behind the mirror as the object is in front.

	<a href="/img/notes/02/locating-image.png" target="_blank"><img src="/img/notes/02/locating-image.png" alt="Light, figure 5" /></a>

	<h2 id="light">Light</h2>

	When light encounters a material, it could be transmitted (pass through), reflected, absorbed or scattered by the material:

	<a href="/img/notes/02/transparant.png" target="_blank"><img src="/img/notes/02/transparant.png" alt="Light, figure 1" /></a>

	<a href="/img/notes/02/translucent.png" target="_blank"><img src="/img/notes/02/translucent.png" alt="Light, figure 2" /></a>

	<a href="/img/notes/02/opaque.png" target="_blank"><img src="/img/notes/02/opaque.png" alt="Light, figure 3" /></a>

	<h2 id="refraction">Refraction</h2>

	Refraction happens due to a change in speed. As light travels from one material to another, it changes speed.

	If the light enters parallel to the normal, the change in speed does not produce a noticeable effect. If the light enters at an angle, the change in speed results in a change in direction of the light.

	<a href="/img/notes/02/refraction-gif.gif" target="_blank"><img src="/img/notes/02/refraction-gif.gif" alt="Light, figure 1" /></a>

	As the wave front travels from one material to another at an angle, not all of the wave hits the boundary and changes speed at the same time. This causes the change in direction:

	<a href="/img/notes/02/refraction-wavefronts.png" target="_blank"><img src="/img/notes/02/refraction-wavefronts.png" alt="Light, figure 2" /></a>

	In the diagram, the refracted wave fronts are closer together than the incident wave fronts. The waves have the same frequency but travel at different speeds, so they have different wavelengths (v=fλ).

	<h2 id="apparent-depth">Apparent Depth</h2>

	If you are looking at an object that is underwater, light is traveling from a source, reflecting off the object, and traveling to your eye. As the light leaves the water, it is refracted. Your brain assumes that the light traveled in a straight line, so the object appears to be higher in the water than it actually is. The Archer fish takes this into account when it spits water at insects!

	<a href="/img/notes/02/apparant-depth-1024x621.png" target="_blank"><img src="/img/notes/02/apparant-depth-1024x621.png" alt="Light, figure 1" /></a>

	<h2 id="lenses">Lenses</h2>

	A lens is a curved material that uses refraction of light to form an image. A convex (or converging) lens is thicker in the middle than at the edges. A concave (or diverging) lens is thinner in the middle than at the edges.

	<a href="/img/notes/02/lenses.png" target="_blank"><img src="/img/notes/02/lenses.png" alt="Light, figure 1" /></a>

	Convex (Converging) Lens

	A convex lens causes parallel rays of light to converge to a point. The point where the rays meet is the focal point or principal focus. The distance from the center of the lens to the focal point is the focal length.

	<a href="/img/notes/02/cconvex.png" target="_blank"><img src="/img/notes/02/cconvex.png" alt="Light, figure 2" /></a>

	Concave (Diverging) Lens

	A concave lens causes parallel rays of light to spread out (diverge). The point where the rays appear to come from is the focal point:

	<a href="/img/notes/02/cconcave.png" target="_blank"><img src="/img/notes/02/cconcave.png" alt="Light, figure 3" /></a>

	Magnification = image height ÷ object height

	<h2 id="constructing-ray-diagrams">Constructing Ray Diagrams</h2>

	When drawing ray diagrams:

	<ol>
		<li>Draw straight lines using a ruler</li>
		<li>Use arrows to show the direction</li>
		<li>Draw to scale</li>
		<li>Use correct symbols for convex and concave lenses:</li>
	</ol>

	<a href="/img/notes/02/lens-symbols.png" target="_blank"><img src="/img/notes/02/lens-symbols.png" alt="Light, figure 1" /></a>

	Draw 3 rays of light to construct your image:

	1 - Parallel to axis – refracted through focal point

	<a href="/img/notes/02/ray-diagrams-1.png" target="_blank"><img src="/img/notes/02/ray-diagrams-1.png" alt="Light, figure 2" /></a>

	2 - Straight through the center of the lens (not refracted)

	<a href="/img/notes/02/ray-diagrams-2.png" target="_blank"><img src="/img/notes/02/ray-diagrams-2.png" alt="Light, figure 3" /></a>

	3 - Through the focal point before the lens – refracted parallel to axis

	<a href="/img/notes/02/ray-diagrams-3.png" target="_blank"><img src="/img/notes/02/ray-diagrams-3.png" alt="Light, figure 4" /></a>

	<ol>
		<li>The image is produced where the 3 rays cross</li>
	</ol>

	<a href="/img/notes/02/ray-diagrams-4.png" target="_blank"><img src="/img/notes/02/ray-diagrams-4.png" alt="Light, figure 5" /></a>

	Use the following words to describe images:

	Real – the image could be formed on a screen (the rays of light actually meet at that point)

	Virtual – the image could not be formed on a screen (the rays of light only appear to come from that point)

	Inverted – upside down

	Upright – the same way up as the object

	Diminished – smaller than the object

	Magnified – larger than the object

	Example ray diagrams:

	<a href="/img/notes/02/convex-1.png" target="_blank"><img src="/img/notes/02/convex-1.png" alt="Light, figure 6" /></a>

	<a href="/img/notes/02/convex-2.png" target="_blank"><img src="/img/notes/02/convex-2.png" alt="Light, figure 7" /></a>

	<a href="/img/notes/02/concave.png" target="_blank"><img src="/img/notes/02/concave.png" alt="Light, figure 8" /></a>

	Worked Example

	An object which is 5cm high is 8cm away from a convex lens of focal length 5cm. Construct a ray diagram to calculate the height of the image. Calculate the magnification of the lens.

	<a href="/img/notes/02/lens-example.png" target="_blank"><img src="/img/notes/02/lens-example.png" alt="Light, figure 9" /></a>

	Image is:

	<ol>
		<li>Real</li>
		<li>Inverted</li>
		<li>Magnified</li>
		<li>If the diagram is drawn to scale, the image is approximately 8cm</li>
		<li>Magnification = 8 ÷ 5 = 1.6</li>
	</ol>

	<h2 id="colour">Colour</h2>

	'White' light is made up of different colors called a spectrum. The color of the light depends on the wavelength of that light. A prism can be used to separate white light into a spectrum as the different wavelengths (colors) are refracted by different amounts.

	<a href="/img/notes/02/prism.gif" target="_blank"><img src="/img/notes/02/prism.gif" alt="Light, figure 1" /></a>

	The colors of the spectrum are:

	<ol>
		<li>Red</li>
		<li>Orange</li>
		<li>Yellow</li>
		<li>Green</li>
		<li>Blue</li>
		<li>Indigo</li>
		<li>Violet</li>
	</ol>

	Objects appear to be certain colors because they reflect some wavelengths of light and absorb others.

	<ol>
		<li>White light (containing all colors) hits the red object</li>
		<li>Red light is reflected from the object</li>
		<li>All other colors are absorbed by the object</li>
		<li>The object appears red</li>
	</ol>

	<a href="/img/notes/02/red.png" target="_blank"><img src="/img/notes/02/red.png" alt="Light, figure 2" /></a>

	<ol>
		<li>White light (containing all colors) hits the blue object</li>
		<li>Blue light is reflected from the object</li>
		<li>All other colors are absorbed by the object</li>
		<li>The object appears blue</li>
	</ol>

	<a href="/img/notes/02/blue.png" target="_blank"><img src="/img/notes/02/blue.png" alt="Light, figure 3" /></a>

	Other colors appear when different wavelengths are reflected in different amounts.

	<a href="/img/notes/02/other.png" target="_blank"><img src="/img/notes/02/other.png" alt="Light, figure 4" /></a>

	A white object appears white because all wavelengths are reflected.

	<a href="/img/notes/02/white.png" target="_blank"><img src="/img/notes/02/white.png" alt="Light, figure 5" /></a>

	A black object appears black because no light is reflected.

	<a href="/img/notes/02/black.png" target="_blank"><img src="/img/notes/02/black.png" alt="Light, figure 6" /></a>

	<h2 id="coloured-lights">Colored Lights</h2>

	Objects can appear different colors under colored lights. Under red light, a red object will still appear red as it will reflect red light. Under green light, the red object will appear black as the green light will be absorbed.

	<a href="/img/notes/02/coloured-lights-1.png" target="_blank"><img src="/img/notes/02/coloured-lights-1.png" alt="Light, figure 1" /></a>

	A white object reflects all colors. Under red light, the white object will appear red. Under green light, the white object will appear green.

	<a href="/img/notes/02/coloured-lights-2.png" target="_blank"><img src="/img/notes/02/coloured-lights-2.png" alt="Light, figure 2" /></a>

	<h2 id="colour-filters">Color Filters</h2>

	A color filter absorbs some wavelengths of light and transmits others. A blue filter allows blue light to pass through but absorbs other colors.

	<a href="/img/notes/02/filters.png" target="_blank"><img class="img-30" src="/img/notes/02/filters.png" alt="Light, figure 1" /></a>

	<dl>
		<dt>What is the name of a lens which converges rays of light to a focal point?</dt>
		<dd id="Colour-Filters0" class="js-click-to-reveal">Convex</dd>
		<dt>What is the name of a lens which diverges rays of light from a focal point?</dt>
		<dd id="Colour-Filters1" class="js-click-to-reveal">Concave</dd>
		<dt>What color will a yellow flag appear to be under red light?</dt>
		<dd id="Colour-Filters2" class="js-click-to-reveal">Black</dd>
		<dt>What color will a white flag appear to be under red light?</dt>
		<dd id="Colour-Filters3" class="js-click-to-reveal">Red</dd>
		<dt>What is the name for the effect of light changing direction as it travels from one medium to another?</dt>
		<dd id="Colour-Filters4" class="js-click-to-reveal">Refraction</dd>
	</dl>
</main>

Light

<header>
			<h1 class="blog-post__title">Electromagnetic Spectrum</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="electromagnetic-spectrum">Electromagnetic Spectrum</h2>

The spectrum of visible light is 7 colours (red - violet). This spectrum actually extends beyond both red and violet (invisible). This wider spectrum is known as the electromagnetic spectrum.

Electromagnetic waves are transverse waves and they travel at the speed of light through a vacuum.

<img src="/img/notes/02/em-spectrum.png" alt="Electromagnetic Spectrum, figure 1" /></a>

Some types of radiation have enough energy to remove electrons from atoms. This is known as ionisation. Ionising radiation can damage cells, leading to cancer. If the dose is high enough, they can kill cells.

<img src="/img/notes/02/ionisation-2.png" alt="Electromagnetic Spectrum, figure 2" /></a>

Gamma, X-rays and Ultraviolet are ionising radiation.

You need to be familiar with the uses and risks of each type of radiation.

Gamma:

<img src="/img/notes/02/gamma.png" alt="Electromagnetic Spectrum, figure 3" /></a>

X-rays:

<img src="/img/notes/02/xrays.png" alt="Electromagnetic Spectrum, figure 4" /></a>

Ultraviolet:

<img src="/img/notes/02/UV.png" alt="Electromagnetic Spectrum, figure 5" /></a>

Visible Light:

<img src="/img/notes/02/visible.png" alt="Electromagnetic Spectrum, figure 6" /></a>

Infra-red:

<img src="/img/notes/02/IR.png" alt="Electromagnetic Spectrum, figure 7" /></a>

Microwaves:

<img src="/img/notes/02/microwaves.png" alt="Electromagnetic Spectrum, figure 8" /></a>

Radiowaves:

<img src="/img/notes/02/radiowaves.png" alt="Electromagnetic Spectrum, figure 9" /></a>

<h2 id="infra-red">Infra-Red</h2>

All objects emit and absorb IR radiation. The higher the temperature of an object, the more infrared radiation it emits in a given time.

A body (object) at a constant temperature is emitting the same amount of radiation that it is absorbing.

<img src="/img/notes/02/IR1.png" alt="Electromagnetic Spectrum, figure 1" /></a>

The amount of radiation entering/leaving a body will determine what happens to it’s temperature.

<img src="/img/notes/02/IR2.png" alt="Electromagnetic Spectrum, figure 2" /></a>

<img src="/img/notes/02/IR3.png" alt="Electromagnetic Spectrum, figure 3" /></a>

Dark, matt colours are best at absorbing and emitting IR radiation.

Light, shiny surfaces are more likely to reflect IR radiation.

A ‘black body’ absorbs all the radiation that it receives, it does not reflect or transmit any radiation. A ‘black body’ is also the best possible emitter of radiation.

An object at a constant temperature emits a range of wavelengths of radiation. The peak intensity emitted depends on the temperature. As the temperature increases, the intensity at every wavelength increases AND the peak intensity will be at a shorter wavelength.

<img src="/img/notes/02/black-body.png" alt="Electromagnetic Spectrum, figure 4" /></a>

<h2 id="non-ionising-radiation">Non-ionising Radiation</h2>

Non-ionising radiation can not cause cancer, although there are other risks.

Visible Light

<img src="/img/notes/02/light-bulb.png" alt="Electromagnetic Spectrum, figure 1" /></a>

Benefits:

<ol>
 <li>Seeing!</li>
 <li>Cameras</li>
 <li>Telescopes</li>
</ol>

Risks:

<ol>
 <li>Blindness</li>
</ol>

<h2 id="ionising-radiation">Ionising Radiation</h2>

Ultraviolet

Ultraviolet is produced by very hot objects. Most of the UV radiation we are exposed to comes from the sun. UV is absorbed by the skin.

Benefits:

<ol>
 <li>Vitamin D is produced by the skin when it absorbs radiation</li>
 <li>UV causes the body to release chemicals that can improve your mood</li>
 <li>Skin that absorbs UV will tan (become a darker colour). Some people see this as a benefit of UV exposure, while others think it is not worth the risks.</li>
</ol>

Risks:

<ol>
 <li>Sunburn – Skin can burn from UV exposure</li>
 <li>Skin Cancer – Exposure to UV over a long period of time increases the risk of skin cancer.</li>
</ol>

X-Rays

X rays will pass through soft tissue but not through more dense material like bones. This can be used to develop images of bones or to view the inside of luggage at an airport.

<img src="/img/notes/02/x-ray-1.png" alt="Electromagnetic Spectrum, figure 1" /></a><img src="/img/notes/02/x-ray-2.png" alt="Electromagnetic Spectrum, figure 2" /></a>

Exposure to X-rays increases the risk of cancer. For a patient, the benefit of having an X-ray to get an accurate diagnosis outweighs the very small increased risk of cancer. For medical staff who work with X-ray machines, precautions are necessary to prevent high levels of exposure:

Precautions:

<ol>
 <li>Only use when necessary</li>
 <li>Target at specific body parts</li>
 <li>Operate machine from separate room or behind lead lined screen</li>
</ol>

<img src="/img/notes/02/x-ray-3.png" alt="Electromagnetic Spectrum, figure 3" /></a>

Gamma Rays

Gamma Rays are released from the nucleus of radioactive materials.

<img src="/img/notes/02/gamma-camera.png" alt="Electromagnetic Spectrum, figure 4" /></a>

To use a scan from a gamma camera, the patient swallows a gamma tracer or has it injected into the bloodstream. The camera detects the gamma radiation emitted from the body, producing an image of the body parts containing the tracer.

<img src="/img/notes/02/radiotherapy-1024x681.jpg" alt="Electromagnetic Spectrum, figure 5" /></a>

As ionising radiation is dangerous to cells, it can be used to kill cancerous cells. The radiation is targeted at the tumour, but some damage to healthy cells is inevitable.

Risks

Every activity has some level of risk associated with it (eg crossing the road or drinking a glass of water). A person will do an activity if they believe the benefits outweigh the risks.

This can be complicated based on the way we think about risks. For example, a person may perceive the risk of skin cancer from sunbeds as quite low risk because it is invisible (can’t see yourself developing cancer) and long term (will happen in a few years, not straight away). This may mean that, although the risk is serious, the person is willing to take that risk for the short term benefit of a tan.

<h2 id="required-practical--infrared-radiation">Required Practical – Infrared Radiation</h2>

To investigate the radiation emitted from different types of surface, a Leslie cube can be used. The Leslie cube is filled with hot water and then the temperature is measured at each side (shiny/dull/white/black) over a period of time. The temperature is measured using an infrared thermometer and so it is important to keep the thermometer the same distance from each side.

<img src="/img/notes/02/leslie-cube.png" alt="Electromagnetic Spectrum, figure 1" /></a>

The results of the experiment should confirm that dark/matt surfaces emit the most IR radiation.

Video 1</a>

Video 2</a>

<h2 id="microwaves">Microwaves</h2>

Microwave radiation can be used to heat food:

<ol>
 <li>Microwave radiation is absorbed by water molecules in the food</li>
 <li>Water molecules heat up, turning to steam</li>
 <li>Hot water/steam heats the food</li>
 <li>Internal heating (therefore heats up faster than a normal oven)</li>
</ol>

<img src="/img/notes/02/microwave-oven.png" alt="Electromagnetic Spectrum, figure 1" /></a>

Microwave radiation is also used for mobile phone communications. This is a different frequency of microwave radiation and so it can not be used to cook food! However, some heating of the brain does occur when using a mobile phone. There are no short term risks from this heating but the long term risks of mobile phones are unknown as they have only been in widespread use for the last 20-25 years.

<img src="/img/notes/02/mobile.png" alt="Electromagnetic Spectrum, figure 2" /></a>

<h2 id="radiowaves">Radiowaves</h2>

Radiowaves are used for astronomy and communicating signals from one location to another.

Information can be carried by a radio wave by modulating a carrier wave. The input signal is an alternating current. This is used to vary the amplitude or frequency of a carrier wave (this is called modulation). Amplitude modulation is known as AM, these signals can be transmitted across further distances but are lower quality. Frequency modulation is known as FM, this is higher quality but can not travel as far.

<img src="/img/notes/02/modulation.png" alt="Electromagnetic Spectrum, figure 1" /></a>

The radio waves are absorbed by an aerial producing an alternating current in the receiver. The original signal is then separated from the carrier wave.

<img src="/img/notes/02/radio-flow-chart.png" alt="Electromagnetic Spectrum, figure 2" /></a>

<dl>
	<dt>Which of these types of radiation is ionising? Ultraviolet, Microwaves, Visible light, Infra red</dt>
	<dd id="Radiowaves0" class="js-click-to-reveal">ultraviolet</dd>
	<dt>Which of these types of radiation is non-ionising? Radiowaves, Gamma rays, X rays, Ultraviolet</dt>
	<dd id="Radiowaves1" class="js-click-to-reveal">radiowaves</dd>
	<dt>Which type of electromagnetic radiation has the shortest waves? Gamma Rays, Radio waves, Infra red, Ultraviolet</dt>
	<dd id="Radiowaves2" class="js-click-to-reveal">gamma</dd>
	<dt>Which type of electromagnetic radiation has the longest waves? Radio waves, Gamma Rays, Infra red, Ultraviolet</dt>
	<dd id="Radiowaves3" class="js-click-to-reveal">radiowaves</dd>
	<dt>Which type of radiation is used by mobile phones?</dt>
	<dd id="Radiowaves4" class="js-click-to-reveal">microwaves</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Electromagnetic Spectrum</h1>
</header>

<main class="blog-post__content">
	<h2 id="electromagnetic-spectrum">Electromagnetic Spectrum</h2>

The spectrum of visible light consists of 7 colors (red - violet). However, the electromagnetic spectrum extends beyond both red and violet, making it invisible. The electromagnetic spectrum refers to this wider range of wavelengths.

Electromagnetic waves are transverse waves that travel at the speed of light through a vacuum.

<a href="/img/notes/02/em-spectrum.png" target="_blank"><img src="/img/notes/02/em-spectrum.png" alt="Electromagnetic Spectrum, figure 1" /></a>

Some types of radiation have enough energy to remove electrons from atoms, a process known as ionization. Ionizing radiation can damage cells and potentially lead to cancer. In high doses, it can even kill cells.

<a href="/img/notes/02/ionisation-2.png" target="_blank"><img src="/img/notes/02/ionisation-2.png" alt="Electromagnetic Spectrum, figure 2" /></a>

Gamma rays, X-rays, and ultraviolet radiation are examples of ionizing radiation.

It is important to be familiar with the uses and risks associated with each type of radiation.

Gamma:

<a href="/img/notes/02/gamma.png" target="_blank"><img src="/img/notes/02/gamma.png" alt="Electromagnetic Spectrum, figure 3" /></a>

X-rays:

<a href="/img/notes/02/xrays.png" target="_blank"><img src="/img/notes/02/xrays.png" alt="Electromagnetic Spectrum, figure 4" /></a>

Ultraviolet:

<a href="/img/notes/02/UV.png" target="_blank"><img src="/img/notes/02/UV.png" alt="Electromagnetic Spectrum, figure 5" /></a>

Visible Light:

<a href="/img/notes/02/visible.png" target="_blank"><img class="img-20" src="/img/notes/02/visible.png" alt="Electromagnetic Spectrum, figure 6" /></a>

Infra-red:

<a href="/img/notes/02/IR.png" target="_blank"><img src="/img/notes/02/IR.png" alt="Electromagnetic Spectrum, figure 7" /></a>

Microwaves:

<a href="/img/notes/02/microwaves.png" target="_blank"><img src="/img/notes/02/microwaves.png" alt="Electromagnetic Spectrum, figure 8" /></a>

Radiowaves:

<a href="/img/notes/02/radiowaves.png" target="_blank"><img src="/img/notes/02/radiowaves.png" alt="Electromagnetic Spectrum, figure 9" /></a>

<h2 id="infra-red">Infra-Red</h2>

All objects emit and absorb infrared (IR) radiation. The higher the temperature of an object, the more infrared radiation it emits in a given time.

A body (object) at a constant temperature emits the same amount of radiation that it absorbs.

<a href="/img/notes/02/IR1.png" target="_blank"><img src="/img/notes/02/IR1.png" alt="Electromagnetic Spectrum, figure 1" /></a>

The amount of radiation entering or leaving a body determines its temperature.

<a href="/img/notes/02/IR2.png" target="_blank"><img src="/img/notes/02/IR2.png" alt="Electromagnetic Spectrum, figure 2" /></a>

<a href="/img/notes/02/IR3.png" target="_blank"><img src="/img/notes/02/IR3.png" alt="Electromagnetic Spectrum, figure 3" /></a>

Dark, matte colors are best at absorbing and emitting IR radiation.

Light, shiny surfaces are more likely to reflect IR radiation.

A 'black body' absorbs all the radiation it receives and does not reflect or transmit any radiation. It is also the best possible emitter of radiation.

An object at a constant temperature emits a range of wavelengths of radiation. The peak intensity emitted depends on the temperature. As the temperature increases, the intensity at every wavelength increases and the peak intensity will be at a shorter wavelength.

<a href="/img/notes/02/black-body.png" target="_blank"><img src="/img/notes/02/black-body.png" alt="Electromagnetic Spectrum, figure 4" /></a>

<h2 id="non-ionising-radiation">Non-ionising Radiation</h2>

Non-ionising radiation cannot cause cancer, although there may be other risks associated with it.

Visible Light

<a href="/img/notes/02/light-bulb.png" target="_blank"><img src="/img/notes/02/light-bulb.png" alt="Electromagnetic Spectrum, figure 1" /></a>

Benefits:

<ol>
<li>Allows us to see</li>
<li>Used in cameras</li>
<li>Used in telescopes</li>
</ol>

Risks:

<ol>
<li>Prolonged exposure can cause blindness</li>
</ol>

<h2 id="ionising-radiation">Ionising Radiation</h2>

Ultraviolet

Ultraviolet radiation is produced by very hot objects. Most of the UV radiation we are exposed to comes from the sun. UV radiation is absorbed by the skin.

Benefits:

<ol>
<li>The skin absorbs UV radiation and produces vitamin D</li>
<li>UV radiation can improve mood by causing the body to release certain chemicals</li>
<li>UV exposure can cause the skin to tan, which some people see as a benefit</li>
</ol>

Risks:

<ol>
<li>Excessive exposure can cause sunburn</li>
<li>Long-term exposure increases the risk of skin cancer</li>
</ol>

X-Rays

X-rays can pass through soft tissue but not through denser materials like bones. This property is used to develop images of bones or to view the inside of luggage at an airport.

<a href="/img/notes/02/x-ray-1.png" target="_blank"><img class="img-30" src="/img/notes/02/x-ray-1.png" alt="Electromagnetic Spectrum, figure 1" /></a><a href="/img/notes/02/x-ray-2.png" target="_blank"><img class="img-30" src="/img/notes/02/x-ray-2.png" alt="Electromagnetic Spectrum, figure 2" /></a>

Exposure to X-rays increases the risk of cancer. However, for patients, the benefit of having an X-ray to obtain an accurate diagnosis outweighs the very small increased risk of cancer. Precautions are necessary for medical staff who work with X-ray machines to prevent high levels of exposure:

Precautions:

<ol>
<li>Only use X-rays when necessary</li>
<li>Target specific body parts</li>
<li>Operate the machine from a separate room or behind a lead-lined screen</li>
</ol>

<a href="/img/notes/02/x-ray-3.png" target="_blank"><img src="/img/notes/02/x-ray-3.png" alt="Electromagnetic Spectrum, figure 3" /></a>

Gamma Rays

Gamma rays are released from the nucleus of radioactive materials.

<a href="/img/notes/02/gamma-camera.png" target="_blank"><img src="/img/notes/02/gamma-camera.png" alt="Electromagnetic Spectrum, figure 4" /></a>

In medical imaging, a patient swallows or has a gamma tracer injected into their bloodstream. A gamma camera detects the gamma radiation emitted from the body, producing an image of the body parts containing the tracer.

<a href="/img/notes/02/radiotherapy-1024x681.jpg" target="_blank"><img src="/img/notes/02/radiotherapy-1024x681.jpg" alt="Electromagnetic Spectrum, figure 5" /></a>

Ionising radiation can be used to kill cancerous cells in a process called radiotherapy. The radiation is targeted at the tumor, but some damage to healthy cells is inevitable.

Risks

Every activity carries some level of risk (e.g., crossing the road or drinking a glass of water). People engage in activities if they believe the benefits outweigh the risks.

Perceptions of risk can be complex. For example, a person may perceive the risk of skin cancer from sunbeds as low because it is invisible and long-term. This perception may lead them to take the risk for the short-term benefit of a tan.

<h2 id="required-practical--infrared-radiation">Required Practical – Infrared Radiation</h2>

To investigate the radiation emitted from different types of surfaces, a Leslie cube can be used. The Leslie cube is filled with hot water, and the temperature is measured at each side (shiny/dull/white/black) over a period of time. An infrared thermometer is used to measure the temperature, and it is important to keep the thermometer at the same distance from each side.

<a href="/img/notes/02/leslie-cube.png" target="_blank"><img src="/img/notes/02/leslie-cube.png" alt="Electromagnetic Spectrum, figure 1" /></a>

The results of the experiment should confirm that dark/matte surfaces emit the most IR radiation.

<h2 id="microwaves">Microwaves</h2>

Microwave radiation can be used to heat food:

<ol>
<li>Microwave radiation is absorbed by water molecules in the food</li>
<li>Water molecules heat up, turning into steam</li>
<li>Hot water/steam heats the food</li>
<li>Internal heating occurs, making it faster than a normal oven</li>
</ol>

<a href="/img/notes/02/microwave-oven.png" target="_blank"><img src="/img/notes/02/microwave-oven.png" alt="Electromagnetic Spectrum, figure 1" /></a>

Microwave radiation is also used for mobile phone communications. However, the frequency of microwave radiation used for mobile phones is different and cannot be used to cook food. Some heating of the brain does occur when using a mobile phone, but there are no short-term risks associated with this heating. The long-term risks of mobile phone use are still unknown as they have only been in widespread use for the last 20-25 years.

<h2 id="radiowaves">Radiowaves</h2>

Radiowaves are used in astronomy and for communicating signals from one location to another.

Information can be carried by a radio wave by modulating a carrier wave. The input signal is an alternating current, which is used to vary the amplitude or frequency of a carrier wave (this is called modulation). Amplitude modulation (AM) signals can be transmitted over longer distances but have lower quality. Frequency modulation (FM) signals have higher quality but cannot travel as far.

<a href="/img/notes/02/modulation.png" target="_blank"><img src="/img/notes/02/modulation.png" alt="Electromagnetic Spectrum, figure 1" /></a>

The radio waves are absorbed by an aerial, producing an alternating current in the receiver. The original signal is then separated from the carrier wave.

<a href="/img/notes/02/radio-flow-chart.png" target="_blank"><img src="/img/notes/02/radio-flow-chart.png" alt="Electromagnetic Spectrum, figure 2" /></a>

<dl>
<dt>Which of these types of radiation is ionizing? Ultraviolet, Microwaves, Visible light, Infra red</dt>
<dd id="Radiowaves0" class="js-click-to-reveal">Ultraviolet</dd>
<dt>Which of these types of radiation is non-ionizing? Radiowaves, Gamma rays, X rays, Ultraviolet</dt>
<dd id="Radiowaves1" class="js-click-to-reveal">Radiowaves</dd>
<dt>Which type of electromagnetic radiation has the shortest waves? Gamma Rays, Radio waves, Infra red, Ultraviolet</dt>
<dd id="Radiowaves2" class="js-click-to-reveal">Gamma rays</dd>
<dt>Which type of electromagnetic radiation has the longest waves? Radio waves, Gamma Rays, Infra red, Ultraviolet</dt>
<dd id="Radiowaves3" class="js-click-to-reveal">Radiowaves</dd>
<dt>Which type of radiation is used by mobile phones?</dt>
<dd id="Radiowaves4" class="js-click-to-reveal">Microwaves</dd>
</dl>


</main>

Electromagnetic Spectrum

<header>
			<h1 class="blog-post__title">Magnets and Electromagnets</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="magnetism">Magnetism</h2>

A magnet will attract certain materials:

<ol>
 <li>Iron</li>
 <li>Steel (because it contains iron)</li>
 <li>Nickel</li>
 <li>Cobalt</li>
</ol>

A magnet has two ‘poles’, North and South:

<img src="/img/notes/03/magnet.png" alt="Magnets and Electromagnets, figure 1" /></a>

If two magnets are brought together, like poles will repel while opposite poles will attract:

<img src="/img/notes/03/magnets.png" alt="Magnets and Electromagnets, figure 2" /></a>

The area around a magnet where the magnetic force can be experienced is called the magnetic field.

The magnetic field is strongest where the field lines are closest (at the poles):

<img src="/img/notes/03/magnetic-field.png" alt="Magnets and Electromagnets, figure 3" /></a>

The Earth also has a magnetic field:

<img src="/img/notes/03/Earths_magnetic_field_schematic.png" alt="Magnets and Electromagnets, figure 4" /></a>

Induced Magnetism

When a magnetic material (not a magnet) enters a magnetic field it experiences induced magnetism. When it is removed from the field it is no longer magnetic.

Temporary Magnetism

Magnetic materials can be magnetised by:

<ol>
 <li>Stroking it with a magnet</li>
 <li>Leaving it near to a magnet for a long time</li>
</ol>

Iron loses temporary magnetism easily, steel does not

<h2 id="electromagnetism">Electromagnetism</h2>

A magnetic field exists around a wire that has electric current flowing through it. The field lines are concentric circles around the wire and the field is strongest close to the wire.

<img src="/img/notes/03/wire-940x1024.png" alt="Magnets and Electromagnets, figure 1" /></a>

The corkscrew rule can be used to find the direction of the field around a wire. The thumb points in the direction of the current and the fingers point in the direction of the field. Reversing the direction of the current will reverse the direction of the field.

<img src="/img/notes/03/corkscrew-1024x757.png" alt="Magnets and Electromagnets, figure 2" /></a>

A solenoid is a coil of insulated wire.

This produces a stronger magnetic field than a single wire:

<img src="/img/notes/03/solenoid.png" alt="Magnets and Electromagnets, figure 3" /></a>

The magnetic field around the solenoid is the same shape as the field around a bar magnet except it also passes through the middle of the solenoid.

The North and South poles are determined by the direction of current:

<ol>
 <li>The South pole is where the current flows clockwise</li>
 <li>The North pole is where the current flows anticlockwise</li>
</ol>

<img src="/img/notes/03/solenoid-field.png" alt="Magnets and Electromagnets, figure 4" /></a>

<h2 id="electromagnets">Electromagnets</h2>

An electromagnet is a solenoid wrapped around an iron core. The magnetic field of the solenoid magnetises the iron core when current is flowing.

<img src="/img/notes/03/electromagnet.png" alt="Magnets and Electromagnets, figure 1" /></a>

The advantage of using an electromagnet is that it can be turned on and off

The strength of an electromagnet can be increased by:

<ol>
 <li>Increasing the number of turns of wire</li>
 <li>Increasing the current flowing through the wire</li>
 <li>Warp the wire around an iron core</li>
</ol>

<h2 id="the-electric-bell">The Electric Bell</h2>

<ol>
 <li>When the button is pressed, a current flows through the coil</li>
 <li>The coil attracts the iron bar, causing the clapper to hit the bell</li>
 <li>This also causes the contact to break the circuit</li>
 <li>The electromagnet turns off and the bar moves back to it’s original position, reconnecting the circuit</li>
 <li>The electromagnet turns back on and the cycle repeats</li>
</ol>

<img src="/img/notes/03/electric-bell.gif" alt="Magnets and Electromagnets, figure 1" /></a>

<h2 id="the-relay">The Relay</h2>

<ol>
 <li>A relay uses a low voltage circuit to turn on a higher voltage circuit</li>
 <li>When the switch is pressed, current flows and the electromagnet attracts the iron arm</li>
 <li>The movement of the arm pushes the two contacts together, turning on the second circuit</li>
</ol>

<img src="/img/notes/03/relay.gif" alt="Magnets and Electromagnets, figure 1" /></a>

<h2 id="the-loudspeaker">The Loudspeaker</h2>

<ol>
 <li>The input signal causes an alternating current in the coil</li>
 <li>As the current changes direction, the north and south pole of the coil change</li>
 <li>This will causes the coil to be attracted/repelled from the permanent magnet each time the current changes</li>
 <li>This makes the cone vibrate, producing soundwaves in the air</li>
</ol>

<img src="/img/notes/03/loudspeaker.gif" alt="Magnets and Electromagnets, figure 1" /></a>

<dl>
	<dt>What will happen to a piece of iron that is brought close to a magnet?</dt>
	<dd id="The-Loudspeaker0" class="js-click-to-reveal">attract</dd>
	<dt>What will happen to a north pole of a magnet that is brought close to the south pole of another magnet?</dt>
	<dd id="The-Loudspeaker1" class="js-click-to-reveal">attract</dd>
	<dt>What will happen to a north pole of a magnet that is brought close to the north pole of another magnet?</dt>
	<dd id="The-Loudspeaker2" class="js-click-to-reveal">repel</dd>
	<dt>What is the name of a device which uses an electromagnet in a low voltage circuit to turn on a higher voltage circuit?</dt>
	<dd id="The-Loudspeaker3" class="js-click-to-reveal">relay</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Magnets and Electromagnets</h1>
</header>

<main class="blog-post__content">
	<h2 id="magnetism">Magnetism</h2>

	A magnet will attract certain materials:

	<ol>
		<li>Iron</li>
		<li>Steel (because it contains iron)</li>
		<li>Nickel</li>
		<li>Cobalt</li>
	</ol>

	A magnet has two ‘poles’, North and South:

	<a href="/img/notes/03/magnet.png" target="_blank"><img src="/img/notes/03/magnet.png" alt="Magnets and Electromagnets, figure 1" /></a>

	If two magnets are brought together, like poles will repel while opposite poles will attract:

	<a href="/img/notes/03/magnets.png" target="_blank"><img src="/img/notes/03/magnets.png" alt="Magnets and Electromagnets, figure 2" /></a>

	The area around a magnet where the magnetic force can be experienced is called the magnetic field.

	The magnetic field is strongest where the field lines are closest (at the poles):

	<a href="/img/notes/03/magnetic-field.png" target="_blank"><img src="/img/notes/03/magnetic-field.png" alt="Magnets and Electromagnets, figure 3" /></a>

	The Earth also has a magnetic field:

	<a href="/img/notes/03/Earths_magnetic_field_schematic.png" target="_blank"><img src="/img/notes/03/Earths_magnetic_field_schematic.png" alt="Magnets and Electromagnets, figure 4" /></a>

	Induced Magnetism

	When a magnetic material (not a magnet) enters a magnetic field, it experiences induced magnetism. When it is removed from the field, it is no longer magnetic.

	Temporary Magnetism

	Magnetic materials can be magnetized by:

	<ol>
		<li>Stroking it with a magnet</li>
		<li>Leaving it near a magnet for a long time</li>
	</ol>

	Iron loses temporary magnetism easily, steel does not.

	<h2 id="electromagnetism">Electromagnetism</h2>

	A magnetic field exists around a wire that has electric current flowing through it. The field lines are concentric circles around the wire, and the field is strongest close to the wire.

	<a href="/img/notes/03/wire-940x1024.png" target="_blank"><img src="/img/notes/03/wire-940x1024.png" alt="Magnets and Electromagnets, figure 1" /></a>

	The corkscrew rule can be used to find the direction of the field around a wire. The thumb points in the direction of the current, and the fingers point in the direction of the field. Reversing the direction of the current will reverse the direction of the field.

	<a href="/img/notes/03/corkscrew-1024x757.png" target="_blank"><img src="/img/notes/03/corkscrew-1024x757.png" alt="Magnets and Electromagnets, figure 2" /></a>

	A solenoid is a coil of insulated wire.

	This produces a stronger magnetic field than a single wire:

	<a href="/img/notes/03/solenoid.png" target="_blank"><img src="/img/notes/03/solenoid.png" alt="Magnets and Electromagnets, figure 3" /></a>

	The magnetic field around the solenoid is the same shape as the field around a bar magnet, except it also passes through the middle of the solenoid.

	The North and South poles are determined by the direction of current:

	<ol>
		<li>The South pole is where the current flows clockwise</li>
		<li>The North pole is where the current flows anticlockwise</li>
	</ol>

	<a href="/img/notes/03/solenoid-field.png" target="_blank"><img src="/img/notes/03/solenoid-field.png" alt="Magnets and Electromagnets, figure 4" /></a>

	<h2 id="electromagnets">Electromagnets</h2>

	An electromagnet is a solenoid wrapped around an iron core. The magnetic field of the solenoid magnetizes the iron core when current is flowing.

	<a href="/img/notes/03/electromagnet.png" target="_blank"><img src="/img/notes/03/electromagnet.png" alt="Magnets and Electromagnets, figure 1" /></a>

	The advantage of using an electromagnet is that it can be turned on and off.

	The strength of an electromagnet can be increased by:

	<ol>
		<li>Increasing the number of turns of wire</li>
		<li>Increasing the current flowing through the wire</li>
		<li>Wrapping the wire around an iron core</li>
	</ol>

	<h2 id="the-electric-bell">The Electric Bell</h2>

	<ol>
		<li>When the button is pressed, a current flows through the coil</li>
		<li>The coil attracts the iron bar, causing the clapper to hit the bell</li>
		<li>This also causes the contact to break the circuit</li>
		<li>The electromagnet turns off, and the bar moves back to its original position, reconnecting the circuit</li>
		<li>The electromagnet turns back on, and the cycle repeats</li>
	</ol>

	<a href="/img/notes/03/electric-bell.gif" target="_blank"><img src="/img/notes/03/electric-bell.gif" alt="Magnets and Electromagnets, figure 1" /></a>

	<h2 id="the-relay">The Relay</h2>

	<ol>
		<li>A relay uses a low voltage circuit to turn on a higher voltage circuit</li>
		<li>When the switch is pressed, current flows, and the electromagnet attracts the iron arm</li>
		<li>The movement of the arm pushes the two contacts together, turning on the second circuit</li>
	</ol>

	<a href="/img/notes/03/relay.gif" target="_blank"><img src="/img/notes/03/relay.gif" alt="Magnets and Electromagnets, figure 1" /></a>

	<h2 id="the-loudspeaker">The Loudspeaker</h2>

	<ol>
		<li>The input signal causes an alternating current in the coil</li>
		<li>As the current changes direction, the north and south pole of the coil change</li>
		<li>This causes the coil to be attracted/repelled from the permanent magnet each time the current changes</li>
		<li>This makes the cone vibrate, producing sound waves in the air</li>
	</ol>

	<a href="/img/notes/03/loudspeaker.gif" target="_blank"><img src="/img/notes/03/loudspeaker.gif" alt="Magnets and Electromagnets, figure 1" /></a>

	<dl>
		<dt>What will happen to a piece of iron that is brought close to a magnet?</dt>
		<dd id="The-Loudspeaker0" class="js-click-to-reveal">It will attract.</dd>
		<dt>What will happen to a north pole of a magnet that is brought close to the south pole of another magnet?</dt>
		<dd id="The-Loudspeaker1" class="js-click-to-reveal">They will attract.</dd>
		<dt>What will happen to a north pole of a magnet that is brought close to the north pole of another magnet?</dt>
		<dd id="The-Loudspeaker2" class="js-click-to-reveal">They will repel.</dd>
		<dt>What is the name of a device that uses an electromagnet in a low voltage circuit to turn on a higher voltage circuit?</dt>
		<dd id="The-Loudspeaker3" class="js-click-to-reveal">Relay.</dd>
	</dl>
</main>

Magnets and Electromagnets

Magnetism & Electromagnetism

<header>
			<h1 class="blog-post__title">Electromagnetic Effects</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="the-motor-effect">The Motor Effect</h2>

When a current flows through a wire, it produces a magnetic field around the wire. If the current-carrying wire is near another magnet it will experience a force (attraction/repulsion)

<img src="/img/notes/03/motor-effect-1.png" alt="Electromagnetic Effects, figure 1" /></a>

<h2 id="flemings-left-hand-rule">Fleming’s Left Hand Rule</h2>

The magnetic field, current and force act at right angles to one another. Fleming’s left hand rule can predict the direction of motion.

<img src="/img/notes/03/LHR.png" alt="Electromagnetic Effects, figure 1" /></a>

<ol>
 <li>Thumb – Direction of force</li>
 <li>First Finger – Direction of magnetic field (North to South)</li>
 <li>__Second (middle) finger __– Direction of current</li>
</ol>

<h2 id="electric-motor">Electric Motor</h2>

An electric motor uses a coil of wire in a magnetic field. The current is flowing in different directions in each side of the coil. This means that (according to Fleming’s Left Hand Rule) one side of the coil will move upwards and the other side will move downwards)

<img src="/img/notes/03/motor-effect-2.png" alt="Electromagnetic Effects, figure 1" /></a>

As the sides of the coil experience opposite forces, the coil will rotate. The coil is connected to the circuit using brushes and a split-ring commutator. The brushes allow electricity to be conducted to the coil while also allowing it to move. The split-ring ‘breaks’ and re-connects the circuit every half turn to allow constant rotation.

<img src="/img/notes/03/motor.gif" alt="Electromagnetic Effects, figure 2" /></a>

Electric motors can be made more powerful by:

<ol>
 <li>Increasing the current</li>
 <li>Increasing the length of wire in the magnetic field</li>
 <li>Increasing the strength of the magnetic field</li>
</ol>

<h2 id="magnetic-flux-density">Magnetic Flux Density</h2>

Magnetic flux density is a measurement of the strength of a magnetic field. (You do NOT need to remember this equation for your exam)

<h2 class="ql-align-center">F = B I L</h2>

F = force (N)

B = magnetic flux density (Tesla, T)

__I __= current (A)

L = Length (m)

Worked Example

A wire has a current of 2.2A flowing through it as it passes through a magnetic field of 0.5T. What force will the 0.25m wire experience?

F=BIL

F = 0.5 x 2.2 x 0.25

F = 0.275N

<h2 id="electromagnetic-induction">Electromagnetic Induction</h2>

When a wire is moved through a magnetic field, electric current is induced in the wire

<img src="/img/notes/02/giphy-downsized.gif" alt="Electromagnetic Effects, figure 1" /></a>

Alternator

Electricity can be generated by rotating a magnet inside a coil of wire. This induces a current in the wire. As the magnetic field is changing direction repeatedly (as it turns), the direction of the induced current also changes. Therefore, alternating Current (AC) is produced. This type of generator is called an alternator.

<img src="/img/notes/03/induction.gif" alt="Electromagnetic Effects, figure 2" /></a>

Dynamo / DC Generator

A dynamo generates Direct Current (DC). It is similar to the alternator except it has a split ring commutator, which means that current is only produced in one direction.

This DC varies from 0 to a positive value. This is different to DC from a battery which is a constant positive value.

<img src="/img/notes/03/dynamo.png" alt="Electromagnetic Effects, figure 3" /></a><img src="/img/notes/03/dynamo-dc.png" alt="Electromagnetic Effects, figure 4" /></a>

<h2 id="transformers">Transformers</h2>

A transformer is a device which is used to increase or decrease voltage (potential difference). It consists of two coils of wire (not connected together) wrapped around an iron core.

<img src="/img/notes/03/transformer.png" alt="Electromagnetic Effects, figure 1" /></a>

An alternating current in the primary coil creates an alternating magnetic field around the iron core. The secondary coil is in the alternating magnetic field. This induces an alternating current in the secondary coil. Transformers do not work with DC as the magnetic field does not change.

<img src="/img/notes/03/transformer.gif" alt="Electromagnetic Effects, figure 2" /></a>

<ol>
 <li>a STEP UP transformer increases the voltage. It has more turns on the secondary coil.</li>
 <li>a STEP DOWN transformer decreases the voltage. It has less turns on the secondary coil.</li>
</ol>

The relationship between voltage and the number of turns on the primary and secondary coil can be described using this equation (you do NOT need to remember this equation for your exam):

<img src="/img/notes/03/transformer-eq.png" alt="Electromagnetic Effects, figure 3" /></a>

V = voltage

N = number of turns

P = primary coil

S = secondary coil

Worked Example

A transformer has 200 turns on its primary coil and 50 turns on its secondary coil. The input voltage is 920V.

Vp/Vs = Np/Ns

920/Vs = 200/50

Vs = 920/4

Vs = 230V

<h2 id="transformer-efficiency">Transformer Efficiency</h2>

Transformers are almost 100% efficient. If 100% efficiency is assumed:

<h2 class="ql-align-center">Vp x Ip = Vs x Is</h2>

V = voltage

I = current

P = primary coil

S = secondary coil

Worked Example

A transformer is used to step down an alternating voltage of 230V to 12V for a 2.5A light bulb. Assume that the transformer is 100% efficient and calculate the current in the primary coil of the transformer.

Vp = 230V

Ip = ?

Vs = 12V

Is = 2.5A

230 x Ip = 12 x 2.5

Ip = (12 x 2.5) ÷ 230 = 0.13A

<h2 id="national-grid">National Grid</h2>

The National Grid is a network of wires and pylons connecting power stations and consumers together.

<img src="/img/notes/02/grid-1024x682.jpg" alt="Electromagnetic Effects, figure 1" /></a>

Every power station feeds into the grid and every consumer takes electricity from the grid. Transformers are used to step up voltage from power station to the grid and to step down voltage from the grid to homes (230V)

<img src="/img/notes/02/grid-2.png" alt="Electromagnetic Effects, figure 2" /></a>

High voltages are used between pylons (400,000 V) so that less energy is lost (high voltage = low current at constant power [P=IV])

<dl>
	<dt>A step down transformer for some Christmas lights has 600 turns on the primary coil and 30 turns on the secondary coil. If it is connected to the mains (230V), what voltage is supplied to the lights?</dt>
	<dd id="National-Grid0" class="js-click-to-reveal">Your answer should include: 11.5V / 11.5 Explanation: 11.5V</dd>
	<dt>A transformer with 400 turns on it’s primary coil is used to step down the mains voltage (230V) to 30V. How many turns are on the secondary coil?</dt>
	<dd id="National-Grid1" class="js-click-to-reveal">52</dd>
	<dt>A magnet is pushed into a wire and 2A of current is induced in the wire. What is produced when the magnet is pulled out of the wire?</dt>
	<dd id="National-Grid2" class="js-click-to-reveal">Your answer should include: -2A / -2 Explanation: -2A</dd>
</dl>


		</main>

<header>
	<h1 class="blog-post__title">Electromagnetic Effects</h1>
</header>

<main class="blog-post__content">
	<h2 id="the-motor-effect">The Motor Effect</h2>

	When a current flows through a wire, it produces a magnetic field around the wire. If the current-carrying wire is near another magnet, it will experience a force (attraction/repulsion).

	<a href="/img/notes/03/motor-effect-1.png" target="_blank"><img src="/img/notes/03/motor-effect-1.png" alt="Electromagnetic Effects, figure 1" /></a>

	<h2 id="flemings-left-hand-rule">Fleming’s Left Hand Rule</h2>

	The magnetic field, current, and force act at right angles to one another. Fleming’s left hand rule can predict the direction of motion.

	<a href="/img/notes/03/LHR.png" target="_blank"><img src="/img/notes/03/LHR.png" alt="Electromagnetic Effects, figure 1" /></a>

	<ol>
		<li>Thumb – Direction of force</li>
		<li>First Finger – Direction of magnetic field (North to South)</li>
		<li>Second (middle) finger – Direction of current</li>
	</ol>

	<h2 id="electric-motor">Electric Motor</h2>

	An electric motor uses a coil of wire in a magnetic field. The current is flowing in different directions on each side of the coil. This means that, according to Fleming’s Left Hand Rule, one side of the coil will move upwards and the other side will move downwards.

	<a href="/img/notes/03/motor-effect-2.png" target="_blank"><img src="/img/notes/03/motor-effect-2.png" alt="Electromagnetic Effects, figure 1" /></a>

	As the sides of the coil experience opposite forces, the coil will rotate. The coil is connected to the circuit using brushes and a split-ring commutator. The brushes allow electricity to be conducted to the coil while also allowing it to move. The split-ring ‘breaks’ and re-connects the circuit every half turn to allow constant rotation.

	<a href="/img/notes/03/motor.gif" target="_blank"><img src="/img/notes/03/motor.gif" alt="Electromagnetic Effects, figure 2" /></a>

	Electric motors can be made more powerful by:

	<ol>
		<li>Increasing the current</li>
		<li>Increasing the length of wire in the magnetic field</li>
		<li>Increasing the strength of the magnetic field</li>
	</ol>

	<h2 id="magnetic-flux-density">Magnetic Flux Density</h2>

	Magnetic flux density is a measurement of the strength of a magnetic field. (You do NOT need to remember this equation for your exam)

	<h2 class="ql-align-center">F = B I L</h2>

	F = force (N)

	B = magnetic flux density (Tesla, T)

	I = current (A)

	L = Length (m)

	Worked Example

	A wire has a current of 2.2A flowing through it as it passes through a magnetic field of 0.5T. What force will the 0.25m wire experience?

	F = BIL

	F = 0.5 x 2.2 x 0.25

	F = 0.275N

	<h2 id="electromagnetic-induction">Electromagnetic Induction</h2>

	When a wire is moved through a magnetic field, electric current is induced in the wire.

	<a href="/img/notes/02/giphy-downsized.gif" target="_blank"><img src="/img/notes/02/giphy-downsized.gif" alt="Electromagnetic Effects, figure 1" /></a>

	Alternator

	Electricity can be generated by rotating a magnet inside a coil of wire. This induces a current in the wire. As the magnetic field is changing direction repeatedly (as it turns), the direction of the induced current also changes. Therefore, alternating current (AC) is produced. This type of generator is called an alternator.

	<a href="/img/notes/03/induction.gif" target="_blank"><img src="/img/notes/03/induction.gif" alt="Electromagnetic Effects, figure 2" /></a>

	Dynamo / DC Generator

	A dynamo generates Direct Current (DC). It is similar to the alternator except it has a split-ring commutator, which means that current is only produced in one direction.

	This DC varies from 0 to a positive value. This is different from DC from a battery, which is a constant positive value.

	<a href="/img/notes/03/dynamo.png" target="_blank"><img src="/img/notes/03/dynamo.png" alt="Electromagnetic Effects, figure 3" /></a><a href="/img/notes/03/dynamo-dc.png" target="_blank"><img src="/img/notes/03/dynamo-dc.png" alt="Electromagnetic Effects, figure 4" /></a>

	<h2 id="transformers">Transformers</h2>

	A transformer is a device used to increase or decrease voltage (potential difference). It consists of two coils of wire (not connected together) wrapped around an iron core.

	<a href="/img/notes/03/transformer.png" target="_blank"><img src="/img/notes/03/transformer.png" alt="Electromagnetic Effects, figure 1" /></a>

	An alternating current in the primary coil creates an alternating magnetic field around the iron core. The secondary coil is in the alternating magnetic field. This induces an alternating current in the secondary coil. Transformers do not work with DC as the magnetic field does not change.

	<a href="/img/notes/03/transformer.gif" target="_blank"><img src="/img/notes/03/transformer.gif" alt="Electromagnetic Effects, figure 2" /></a>

	<ol>
		<li>A step-up transformer increases the voltage. It has more turns on the secondary coil.</li>
		<li>A step-down transformer decreases the voltage. It has fewer turns on the secondary coil.</li>
	</ol>

	The relationship between voltage and the number of turns on the primary and secondary coil can be described using this equation (you do NOT need to remember this equation for your exam):

	<a href="/img/notes/03/transformer-eq.png" target="_blank"><img src="/img/notes/03/transformer-eq.png" alt="Electromagnetic Effects, figure 3" /></a>

	V = voltage

	N = number of turns

	P = primary coil

	S = secondary coil

	Worked Example

	A transformer has 200 turns on its primary coil and 50 turns on its secondary coil. The input voltage is 920V.

	Vp/Vs = Np/Ns

	920/Vs = 200/50

	Vs = 920/4

	Vs = 230V

	<h2 id="transformer-efficiency">Transformer Efficiency</h2>

	Transformers are almost 100% efficient. If 100% efficiency is assumed:

	<h2 class="ql-align-center">Vp x Ip = Vs x Is</h2>

	V = voltage

	I = current

	P = primary coil

	S = secondary coil

	Worked Example

	A transformer is used to step down an alternating voltage of 230V to 12V for a 2.5A light bulb. Assume that the transformer is 100% efficient and calculate the current in the primary coil of the transformer.

	Vp = 230V

	Ip = ?

	Vs = 12V

	Is = 2.5A

	230 x Ip = 12 x 2.5

	Ip = (12 x 2.5) ÷ 230 = 0.13A

	<h2 id="national-grid">National Grid</h2>

	The National Grid is a network of wires and pylons connecting power stations and consumers together.

	<a href="/img/notes/02/grid-1024x682.jpg" target="_blank"><img src="/img/notes/02/grid-1024x682.jpg" alt="Electromagnetic Effects, figure 1" /></a>

	Every power station feeds into the grid, and every consumer takes electricity from the grid. Transformers are used to step up voltage from power station to the grid and to step down voltage from the grid to homes (230V).

	<a href="/img/notes/02/grid-2.png" target="_blank"><img src="/img/notes/02/grid-2.png" alt="Electromagnetic Effects, figure 2" /></a>

	High voltages are used between pylons (400,000 V) so that less energy is lost (high voltage = low current at constant power [P=IV]).

	<dl>
		<dt>A step-down transformer for some Christmas lights has 600 turns on the primary coil and 30 turns on the secondary coil. If it is connected to the mains (230V), what voltage is supplied to the lights?</dt>
		<dd id="National-Grid0" class="js-click-to-reveal">Your answer should include: 11.5V / 11.5 Explanation: 11.5V</dd>
		<dt>A transformer with 400 turns on its primary coil is used to step down the mains voltage (230V) to 30V. How many turns are on the secondary coil?</dt>
		<dd id="National-Grid1" class="js-click-to-reveal">52</dd>
		<dt>A magnet is pushed into a wire and 2A of current is induced in the wire. What is produced when the magnet is pulled out of the wire?</dt>
		<dd id="National-Grid2" class="js-click-to-reveal">Your answer should include: -2A / -2 Explanation: -2A</dd>
	</dl>
</main>

Electromagnetic Effects

<header>
			<h1 class="blog-post__title">Space</h1>
		</header>

		<main class="blog-post__content">
			<h2 id="definitions">Definitions</h2>

Star – A ball of hydrogen (and helium) giving out heat and light from nuclear fusion

Planet – A sphere of rock or gas orbiting a star

Dwarf planet – Small ‘planets’ that do not meet all the criteria to be called a planet (i.e. a planet has to be large enough to ‘clear it’s neighborhood’ by gravity pulling in any nearby small objects)

Moon – A sphere of rock orbiting a planet

Asteroid – A lump of rock (may or may not be orbiting anything!)

Comet – A ball of ice, dust and gas orbiting a star in an elliptical orbit

Meteor – A tiny piece of rock

Galaxy – A group of billions of stars

Universe – Everything that exists! Contains billions of galaxies

<h2 id="solar-system">Solar System</h2>

<img src="/img/notes/03/solar-system-1024x576.png" alt="Space, figure 1" /></a>

A solar system consists of a star with objects orbiting it. Our solar system has 8 planets (and some other objects) orbiting our star – the sun.

<img src="/img/notes/03/solar-system-gif.gif" alt="Space, figure 2" /></a>

A satellite is an object that orbits a planet. There are natural satellites such as our moon and artificial satellites, which are man made.

<h2 id="milky-way">Milky Way</h2>

Our solar system is part of a group of billions of stars known as the Milky Way – this is our galaxy. The universe contains billions of galaxies.

<img src="/img/notes/03/milky-way.jpg" alt="Space, figure 1" /></a>

<img src="/img/notes/03/struture-of-universe.png" alt="Space, figure 2" /></a>

<h2 id="red-shift">Red Shift</h2>

The same effect happens with light, when the objects are moving at very high speeds, such as stars.

The light emitted from a star that is moving away from you will be shifted to a lower frequency, moving it to the red end of the spectrum. (Almost) all stars are red shifted. This means that they are all moving away from us (and from each other). This suggests that the universe is expanding.

<img src="/img/notes/03/red-shift-1024x640.png" alt="Space, figure 1" /></a>

More distant galaxies have more red shift than closer galaxies which means the distant galaxies are moving faster.

Big Bang

If the universe is currently expanding, that suggests that the universe used to be smaller and that a force started the expansion. This theory for the beginning of the universe is known of the big bang theory. The big bang theory states that, approximately 14 billion years ago, all the matter in the universe occupied a very small, dense, hot space. This then expanded rapidly outwards (exploded) starting the expansion that we see today.

<dl>
	<dt>Which process causes stars to give out heat and light?</dt>
	<dd id="Red-Shift0" class="js-click-to-reveal">Your answer should include: nuclear / fusion</dd>
	<dt>Light from stars that are moving away from an observer is shifted towards which end of the spectrum?</dt>
	<dd id="Red-Shift1" class="js-click-to-reveal">red</dd>
	<dt>What is the name for a cloud of dust and gas that will be pulled together by gravity to form a star?</dt>
	<dd id="Red-Shift2" class="js-click-to-reveal">nebula</dd>
	<dt>What element takes part in fusion in a star when it is in the main sequence stage?</dt>
	<dd id="Red-Shift3" class="js-click-to-reveal">hydrogen</dd>
	<dt>What is the next stage in the life of a large mass star after it is a super red giant?</dt>
	<dd id="Red-Shift4" class="js-click-to-reveal">supernova</dd>
</dl>

<h2 id="orbits">Orbits</h2>

Planets orbit the sun in almost circular objects. Moons and artificial satellites orbit planets in almost circular objects. Orbits occur due to the force of gravity.

Objects travelling at a constant speed in a circle are changing velocity (because velocity is speed and direction). The motion of the planet would cause it to fly off into space but the force of gravity is attracting the planet towards the sun. the combination of the momentum of the object and the force of gravity towards the centre of the circle means that the planet travels in a circular path around the sun. As there is no friction or air resistance in space, the planet continues at a constant speed in this orbit.

<img src="/img/notes/03/orbit.png" alt="Space, figure 1" /></a>

The gravitational force is stronger, the closer you get to the star/planet. The stronger the force, the faster the orbiting object needs to travel to remain in orbit (rather than being pulled to the centre). If the speed of the object changes, the radius of the orbit will also change. The faster the object, the smaller the radius of the orbit.

<h2 id="life-cycle-of-a-star">Life Cycle of a Star</h2>

__1 - ____Nebula __

Gravity pulls gas cloud of (hydrogen) gas and dust together

2 – ____Protostar

As gravity causes contraction, the particles collide more often and the temperature and pressure increase.

3 -__ Main Sequence __

As the temperature (and therefore the kinetic energy of the particles) increases, eventually nuclear fusion occurs, releasing heat and light. This is called the ‘main sequence’ stage of the life cycle, most of the stars lifetime will be in this stage. The outwards expansion of the star due to fusion is in equilibrium with the inwards contraction of the star due to gravity and so the star remains at a constant size.

Low Mass Stars (i.e. our sun)

4 – ____Red Giant

As the hydrogen runs out, fusion of helium begins. The star expands and cools (red)

5 – ____White dwarf

The red giant becomes unstable and ejects its outer layer of dust and gas, leaving behind a hot, dense core.

6 –__ Black Dwarf__

The white dwarf cools down and eventually stops releasing energy

Large Mass Stars

4 – ____Super Red Giant

As the hydrogen runs out, fusion of helium begins. The star expands and cools (red). Fusion of heavier elements (up to iron) occurs.

5 – ____Supernova

The star contracts and expands a number of times due to nuclear fusion of heavy elements. Eventually the star explodes as a supernova, producing elements heavier than iron and spreading them throughout the universe.

6 – ____Neutron Star or Black Hole

The supernova leaves behind a very dense core called a neutron star. The most massive stars will leave a black hole, which is so dense that not even light can escape its gravity.

<img src="/img/notes/03/life-cycle-of-star.png" alt="Space, figure 1" /></a>

All the naturally occurring elements (see the periodic table) have been created as the products of fusion ion stars and released into the universe via supernovas.

		</main>

<header>
	<h1 class="blog-post__title">Space</h1>
</header>

<main class="blog-post__content">
	<h2 id="definitions">Definitions</h2>

	Star – A ball of hydrogen (and helium) giving out heat and light from nuclear fusion.

	Planet – A sphere of rock or gas orbiting a star.

	Dwarf planet – Small ‘planets’ that do not meet all the criteria to be called a planet (i.e. a planet has to be large enough to ‘clear its neighborhood’ by gravity pulling in any nearby small objects).

	Moon – A sphere of rock orbiting a planet.

	Asteroid – A lump of rock (may or may not be orbiting anything!).

	Comet – A ball of ice, dust, and gas orbiting a star in an elliptical orbit.

	Meteor – A tiny piece of rock.

	Galaxy – A group of billions of stars.

	Universe – Everything that exists! Contains billions of galaxies.

	<h2 id="solar-system">Solar System</h2>

	<a href="/img/notes/03/solar-system-1024x576.png" target="_blank"><img src="/img/notes/03/solar-system-1024x576.png" alt="Space, figure 1" /></a>

	A solar system consists of a star with objects orbiting it. Our solar system has 8 planets (and some other objects) orbiting our star – the sun.

	<a href="/img/notes/03/solar-system-gif.gif" target="_blank"><img src="/img/notes/03/solar-system-gif.gif" alt="Space, figure 2" /></a>

	A satellite is an object that orbits a planet. There are natural satellites such as our moon and artificial satellites, which are man-made.

	<h2 id="milky-way">Milky Way</h2>

	Our solar system is part of a group of billions of stars known as the Milky Way – this is our galaxy. The universe contains billions of galaxies.

	<a href="/img/notes/03/milky-way.jpg" target="_blank"><img src="/img/notes/03/milky-way.jpg" alt="Space, figure 1" /></a>

	<a href="/img/notes/03/struture-of-universe.png" target="_blank"><img src="/img/notes/03/struture-of-universe.png" alt="Space, figure 2" /></a>

	<h2 id="red-shift">Red Shift</h2>

	The same effect happens with light when the objects are moving at very high speeds, such as stars.

	The light emitted from a star that is moving away from you will be shifted to a lower frequency, moving it to the red end of the spectrum. (Almost) all stars are red-shifted. This means that they are all moving away from us (and from each other). This suggests that the universe is expanding.

	<a href="/img/notes/03/red-shift-1024x640.png" target="_blank"><img src="/img/notes/03/red-shift-1024x640.png" alt="Space, figure 1" /></a>

	More distant galaxies have more red shift than closer galaxies, which means the distant galaxies are moving faster.

	Big Bang

	If the universe is currently expanding, that suggests that the universe used to be smaller and that a force started the expansion. This theory for the beginning of the universe is known as the Big Bang theory. The Big Bang theory states that approximately 14 billion years ago, all the matter in the universe occupied a very small, dense, hot space. This then expanded rapidly outwards (exploded), starting the expansion that we see today.

	<dl>
		<dt>Which process causes stars to give out heat and light?</dt>
		<dd id="Red-Shift0" class="js-click-to-reveal">Your answer should include: nuclear / fusion</dd>
		<dt>Light from stars that are moving away from an observer is shifted towards which end of the spectrum?</dt>
		<dd id="Red-Shift1" class="js-click-to-reveal">red</dd>
		<dt>What is the name for a cloud of dust and gas that will be pulled together by gravity to form a star?</dt>
		<dd id="Red-Shift2" class="js-click-to-reveal">nebula</dd>
		<dt>What element takes part in fusion in a star when it is in the main sequence stage?</dt>
		<dd id="Red-Shift3" class="js-click-to-reveal">hydrogen</dd>
		<dt>What is the next stage in the life of a large mass star after it is a super red giant?</dt>
		<dd id="Red-Shift4" class="js-click-to-reveal">supernova</dd>
	</dl>

	<h2 id="orbits">Orbits</h2>

	Planets orbit the sun in almost circular objects. Moons and artificial satellites orbit planets in almost circular objects. Orbits occur due to the force of gravity.

	Objects traveling at a constant speed in a circle are changing velocity (because velocity is speed and direction). The motion of the planet would cause it to fly off into space, but the force of gravity is attracting the planet towards the sun. The combination of the momentum of the object and the force of gravity towards the center of the circle means that the planet travels in a circular path around the sun. As there is no friction or air resistance in space, the planet continues at a constant speed in this orbit.

	<a href="/img/notes/03/orbit.png" target="_blank"><img src="/img/notes/03/orbit.png" alt="Space, figure 1" /></a>

	The gravitational force is stronger the closer you get to the star/planet. The stronger the force, the faster the orbiting object needs to travel to remain in orbit (rather than being pulled to the center). If the speed of the object changes, the radius of the orbit will also change. The faster the object, the smaller the radius of the orbit.

	<h2 id="life-cycle-of-a-star">Life Cycle of a Star</h2>

	1 - Nebula

	Gravity pulls gas cloud of (hydrogen) gas and dust together.

	2 – Protostar

	As gravity causes contraction, the particles collide more often and the temperature and pressure increase.

	3 - Main Sequence

	As the temperature (and therefore the kinetic energy of the particles) increases, eventually nuclear fusion occurs, releasing heat and light. This is called the ‘main sequence’ stage of the life cycle. Most of the star's lifetime will be in this stage. The outwards expansion of the star due to fusion is in equilibrium with the inwards contraction of the star due to gravity, so the star remains at a constant size.

	Low Mass Stars (i.e. our sun)

	4 – Red Giant

	As the hydrogen runs out, fusion of helium begins. The star expands and cools (red).

	5 – White dwarf

	The red giant becomes unstable and ejects its outer layer of dust and gas, leaving behind a hot, dense core.

	6 – Black Dwarf

	The white dwarf cools down and eventually stops releasing energy.

	Large Mass Stars

	4 – Super Red Giant

	As the hydrogen runs out, fusion of helium begins. The star expands and cools (red). Fusion of heavier elements (up to iron) occurs.

	5 – Supernova

	The star contracts and expands a number of times due to nuclear fusion of heavy elements. Eventually, the star explodes as a supernova, producing elements heavier than iron and spreading them throughout the universe.

	6 – Neutron Star or Black Hole

	The supernova leaves behind a very dense core called a neutron star. The most massive stars will leave a black hole, which is so dense that not even light can escape its gravity.

	<a href="/img/notes/03/life-cycle-of-star.png" target="_blank"><img src="/img/notes/03/life-cycle-of-star.png" alt="Space, figure 1" /></a>

	All the naturally occurring elements (see the periodic table) have been created as the products of fusion in stars and released into the universe via supernovas.

</main>

GCSE AQA Physics - Electricity

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Contents

Static Electricity

Static Electricity

Induced Charge

Van der Graaff Generator