Q: What is a microphone and how does it work to convert sound into electrical signals?
A: A microphone is a device that converts sound waves into electrical signals using the generator effect, also known as electromagnetic induction. In a moving-coil microphone, the pressure variations in sound waves cause a flexible diaphragm to vibrate. These vibrations make a coil of wire, which is attached to the diaphragm, move within a magnetic field. The movement of the coil relative to the magnet induces a potential difference in the coil. If the coil is part of a complete circuit, the induced potential difference causes a current to flow. The size and direction of this current change as the coil vibrates, producing electrical signals that match the pressure variations in the original sound waves.
Q: Define the generator effect and explain how it induces a potential difference.
A: The generator effect, also known as electromagnetic induction, occurs when an electrical conductor, such as a wire, experiences motion relative to a magnetic field or is exposed to a changing magnetic field. This movement induces a potential difference (voltage) across the conductor. If the conductor is part of a complete circuit, an electric current is also produced. The induced current generates a magnetic field around itself, which opposes the original change in the magnetic field that created it. The direction of the induced current can be reversed by moving the conductor or magnet in the opposite direction or by reversing the polarity of the magnet.
Q: Give examples of situations where the generator effect occurs.
A: Examples of the generator effect include:
Moving a wire through a magnetic field.
Moving a magnet into or out of a coil of wire.
Moving a magnet side to side in a coil to create brief current changes.
Rotating a magnet end-to-end inside a coil or rotating a coil within a magnetic field, as done in generators.
Q: How can the magnitude of an induced potential difference be increased?
A: The induced potential difference or current can be increased by:
Increasing the speed of motion of the magnet or conductor, which causes more magnetic field lines to be cut per second.
Increasing the strength of the magnetic field, creating more field lines for the conductor to cut.
Increasing the number of turns in the coil, allowing more of the conductor to interact with the magnetic field.
Q: What is electromagnetic induction and how is it related to the generator effect?
A: Electromagnetic induction is the production of a potential difference (voltage) when a conductor, such as a wire, moves through a magnetic field or is exposed to a changing magnetic field. If the conductor is part of a complete circuit, an induced current will flow. This process is synonymous with the generator effect, where motion between a conductor and a magnetic field generates electricity.
Q: Explain how an alternating current (ac) generator, or alternator, produces electricity.
A: An alternator is a type of generator that produces an alternating potential difference and current. It consists of a coil of wire rotating within a magnetic field, or a magnet rotating inside a coil. As the coil spins, a potential difference is induced in the coil. The coil is attached to slip rings, which rotate with it, while brushes maintain continuous contact with the external circuit. The current changes direction every half turn, producing an alternating current (ac). The maximum potential difference is reached when the coil moves at 90° to the magnetic field, while no potential difference is induced when the coil is parallel to the field.
Q: How can the output of an alternator be increased?
A: The output of an alternator can be increased by:
Increasing the rate of rotation of the coil.
Increasing the strength of the magnetic field.
Increasing the number of turns on the coil.
Q: Describe the key positions of the coil in an alternator and the corresponding induced potential difference.
A: In an alternator:
At 0°, the coil moves parallel to the magnetic field, so no potential difference is induced.
At 90°, the coil moves perpendicular to the field, producing maximum induced potential difference.
At 180°, the coil is again parallel to the field, so no potential difference is induced.
At 270°, the coil is perpendicular again, producing maximum potential difference in the opposite direction to 90°.
At 360°, the coil completes a full rotation, returning to no induced potential difference as it is parallel to the field.
Q: Explain how a direct current (dc) generator, or dynamo, differs from an alternator.
A: A dynamo is a type of dc generator that produces a direct potential difference and current. Like an alternator, it has a coil of wire rotating in a magnetic field, but it uses a split-ring commutator instead of slip rings. The split-ring commutator swaps the connections every half turn to prevent the current from reversing direction, ensuring that the current in the external circuit always flows in the same direction.
Q: How can the output of a dynamo be increased?
A: The output of a dynamo can be increased by:
Increasing the rate of rotation of the coil.
Increasing the strength of the magnetic field.
Increasing the number of turns on the coil.
Q: Describe the key positions of the coil in a dynamo and the corresponding induced potential difference.
A: In a dynamo:
At 0°, the coil moves parallel to the magnetic field, so no potential difference is induced.
At 90°, the coil moves perpendicular to the field, producing maximum induced potential difference.
At 180°, the coil is parallel to the field, so no potential difference is induced.
At 270°, the coil moves perpendicular to the field again, producing maximum potential difference in the same direction as at 90°.
At 360°, the coil completes a full rotation and returns to moving parallel to the field, so no potential difference is induced.
Q: How can oscilloscopes be used to observe the potential difference generated by alternators and dynamos?
A: Oscilloscopes display the changing potential difference over time. For an alternator, the line on the screen oscillates above and below the horizontal axis, showing alternating current. For a dynamo, the line remains above the horizontal axis, showing direct current. The height of the line at any point corresponds to the instantaneous potential difference. Increasing the rotation speed increases the overall potential difference and produces more peaks on the graph.
Q: How does the induced current oppose the change that created it?
A: When a current is induced in a conductor, it generates a magnetic field around itself. This induced magnetic field acts against the original change in the magnetic field that produced the current, whether it was the motion of a conductor or a changing magnetic field. This opposition is consistent with Lenz’s law, meaning the induced current always works to counteract the change that created it.
Q: Explain the detailed process of electromagnetic induction in moving a magnet into a coil.
A: When a magnet is moved into a coil of wire connected to an ammeter, the changing magnetic field induces a potential difference, producing a current in the circuit. The ammeter shows positive current as the magnet enters the coil. If the magnet stops inside the coil, no current flows. When the magnet is pulled out, the ammeter shows negative current, indicating that the direction of the induced current has reversed. This demonstrates that the direction of the induced current depends on the relative motion of the magnet and coil, and can be reversed by changing the direction of motion or the polarity of the magnet.
Source 1: Microphones:
Microphones are devices that convert the pressure variations in sound waves into a potential difference or current.
The sound waves cause the diaphragm to vibrate.
This causes the coil of wire to move through the magnetic field which leads to a potential difference being induced.
||| The Generator Effect:
The generator effect is when an electrical conductor (such as a wire) induces (creates) a potential difference across when it either:
- moves relative to a magnetic field, or
- experiences a change in magnetic field.
If the conductor is part of a complete circuit, it also induces a current in the conductor.
You can think of the generator effect as the opposite of the motor effect.
Examples of the generator effect are:
- moving a wire through a magnetic field
- moving magnets through a solenoid so that the wire experiences a change in magnetic field
If the generator effect occurs in a complete circuit and a current is induced, the current created opposes the original change that created it.
For example, if you move a wire downwards through a magnetic field to induce a potential difference and current, the wire would experience a force upwards to oppose the downwards motion. The potential difference induced can be increased by:
- increasing the speed of the motion of the magnet or conductor.
- increasing the strength of the magnet.
- increasing the number of turns in the solenoid.
The direction of the current induced can reversed by:
- moving the wire or conductor in the opposite direction
- switching the orientation of the poles on the magnet
||| Generators:
Generators are used to create electricity using magnets and conductors.
They do the opposite of what motors do- they are rotated so that the wires experience a change in magnetic field.
This induces a potential difference, and if it is connected to a complete circuit it induces a current too.
There are two types of generators:
- Alternators:
These use slip rings to generate an alternating potential difference and current.
The slip rings are used to stop the wires from twisting together.
- Dynamos:
These use split ring commutators to generate a direct potential difference and current.
The split ring commutator switches the current every half turn to convert the alternating current into direct current. /////////// Source 2: Induced potential and the generator effect:
A potential difference or voltage is needed to make an electric current flow in a circuit:
- a coil of wire is moved in a magnetic field
- a magnet is moved into a coil of wire
This is called electromagnetic induction (which is the production of a potential difference (voltage) when a conductor, such as a wire, is moved through a magnetic field or exposed to a varying magnetic field; if the conductor is part of an electric circuit, an induced current will flow) and is often referred to as the generator effect (which is when motion between a conductor and a magnetic field creates electricity, ie a magnet is moved into a coil of wire).
The induced voltage produces an induced current if the conductor is connected in a complete circuit. As with all currents, the induced current creates a magnetic field around itself. Note that this magnetic field opposes the original change. For example, if a magnet is moved into a coil of wire, the
induced magnetic field tends to repel the magnet back out of the coil. This effect occurs whether a magnet is moved into a coil, or a coil is moved around a magnet.
Factors affecting the induced potential:
The direction of the induced current depends on the direction of movement of the magnet relative to the coil. The current is reversed when:
- the magnet is moved out of the coil
- the other pole of the magnet is moved into the coil
The following describes how this works: A bar magnet rests outside a wire coil connected to an ammeter showing no current. The magnet moves into the coil of wire and the ammeter registers positive current flow. The magnet is stationary within the coil of wire, there is no current flow. The magnet moves out of the coil of wire and the ammeter registers negative current flow. || An induced potential difference or induced current will increase if:
- the speed of movement is increased
- the magnetic field strength is increased
- the number of turns on the coil is increased ||| The ac generator:
A generator is a device that converts kinetic energy into electrical energy. An alternating current (ac) generator i is a device that produces a potential difference . A simple ac generator consists of a coil of wire rotating in a magnetic field. Cars use a type of ac generator, called an alternator (which is an electrical generator which produces alternating current, an ac generator), to keep the battery charged and to run the electrical system while the engine is working. ||| The alternator:
The following describes a simple alternator: First, the coil is rotated in the magnetic field, which causes current to be induced in the rotating coil. This coil is attached to slip rings connected to the coil, which rotate along with it. To transfer the electricity, brushes make continuous contact between the external circuit and the slip rings. As a result, the current flows in the external circuit. Slip rings maintain constant contact with the same sides of the coil.
As one side of the coil moves up through the magnetic field, a potential difference is induced in one direction. As the rotation continues and that side of the coil moves down, the induced potential difference reverses direction. This means that the alternator produces a current that is constantly changing. This is alternating current or ac. ||| Alternator output on a graph:
The output of an alternator as it rotates can be represented on a potential difference-time graph with potential difference (voltage) on the vertical axis and time on the horizontal axis.
The graph is an alternating sine curve. The maximum potential difference or current can be increased by:
- increasing the rate of rotation
- increasing the strength of the magnetic field
- increasing the number of turns on the coil
The following lists four key different positions of the coil in an alternator, and the corresponding potential difference produced: When the coil is at 0°, it moves parallel to the direction of the magnetic field, so no potential difference is induced. As it rotates to 90°, the coil moves at 90° to the field, causing the induced potential difference to reach its maximum. At 180°, the coil is again moving parallel to the magnetic field, meaning no potential difference is induced. Once it reaches 270°, the coil moves at 90° to the field again for maximum induced potential difference, though it now travels in the opposite direction compared to its position at 90°. Finally, at 360°, the coil completes a full rotation and returns to its starting point where it moves parallel to the field, resulting in no induced potential difference. ||| The dc generator:
A direct current (dc) generator is another device that produces a potential difference. A simple dc generator consists of a coil of wire rotating in a magnetic field. However, it uses a split ring commutator rather than the two slip rings found in alternating current (ac) generators. Some bike
lights use a type of dc generator called a dynamo (which is an electrical generator which produces direct current, a dc generator) to run the lamps while the wheels are turning. ||| The dynamo: In a dynamo, a split ring commutator changes the coil connections every half turn. As the induced potential difference is about to change direction, the connections are reversed. This means that the current to the external circuit always flows in the same direction. For example, in a bike dynamo, the magnet rotates inside a fixed coil of wire. ||| Dynamo output on a graph:
The output of a rotating dynamo can be shown on a potential difference-time graph. The graph shows a sine curve that stays in the same direction all the time. The maximum potential difference or current can be increased by: - increasing the rate of rotation
- increasing the strength of the magnetic field
- increasing the number of turns on the coil
The following lists four key different positions of the coil in a dynamo, and the corresponding potential difference produced: When the coil is at 0°, it moves parallel to the direction of the magnetic field, so no potential difference is induced. As the coil rotates to 90°, it moves at 90° to the field, causing the induced potential difference to reach its maximum. At 180°, the coil returns to moving parallel to the magnetic field, meaning no potential difference is induced. Once it reaches 270°, the coil is again moving at 90° to the field for maximum induced potential difference, but in this case, the potential difference travels in the same direction as it did at 90°. Finally, at 360°, the coil completes its full rotation and returns to its starting point, moving parallel to the magnetic field so that no potential difference is induced. ||| Microphones:
The microphone is a device that converts sound waves into electrical signals. Microphones use the
generator effect to induce a changing current from the pressure variations of sound waves. ||| Moving-coil microphones:
A moving-coil microphone is a microphone in which electrical signals are produced when the pressure variations in sound waves vibrate a coil of wire within a magnetic field. In a moving-coil microphone:
- pressure variations in sound waves cause the flexible diaphragm to vibrate
- the vibrations of the diaphragm cause vibrations in the coil
- the coil moves relative to a permanent magnet, so a potential difference is induced in the coil
- the coil is part of a complete circuit, so the induced potential difference causes a current to flow around the circuit
- the changing size and direction of the induced current matches the vibrations of the coil
- the electrical signals generated match the pressure variations in the sound waves //////////// Source 3: The Generator Effect:
Electricity is generated using the generator effect (which is also known as electromagnetic induction).
||| Cutting Field Lines Induces a Potential Difference:
The Generator Effect: The induction of a potential difference (and current if there’s a complete circuit) in a wire which is moving relative to a magnetic field, or experiencing a change in magnetic field.
The generator effect creates a potential difference in a conductor, and a current if the conductor is part of a complete circuit.
You can do this by moving a magnet in a coil of wire OR moving a conductor (wire) in a magnetic field (“cutting” magnetic field lines).
Shifting the magnet from side to side creates a little “blip” of current if the conductor is part of a complete circuit.
If you move the magnet (or conductor) in the opposite direction, then the potential difference/current will be reversed. Likewise if the polarity of the magnet is reversed, then the potential difference/current will be reversed too.
If you keep the magnet (or the coil) moving backwards and forwards, you produce a potential difference that keeps swapping direction — an alternating current.
You can create the same effect by turning a magnet end to end in a coil, or turning a coil inside a magnetic field. This is how generators work to produce ac or direct current (dc).
As you turn the magnet, the magnetic field through the coil changes. This change in the magnetic field induces a potential difference, which can make a current flow in the wire.
When you’ve turned the magnet through half a turn, the direction of the magnetic field through the coil reverses. When this happens, the potential difference reverses, so the current flows in the opposite direction around the coil of wire.
If you keep turning the magnet in the same direction — always clockwise, say — then the potential difference will keep on reversing every half turn and you’ll get an alternating current.
||| Induced Current Opposes the Change that Made It:
So, a change in magnetic field can induce a current in a wire. But when a current flows through a wire, a magnetic field is created around the wire. (That’s a second magnetic field — different to the one whose field lines were being cut in the first place.)
The magnetic field created by an induced current always acts against the change that made it (whether that’s the movement of a wire or a change in the field it’s in). Basically, it’s trying to return things to the way they were.
This means that the induced current always opposes the change that made it.
||| You Can Change the Size of the Induced Potential Difference:
If you want to change the size of the induced pd, you have to change the rate that the magnetic field is changing. Induced potential difference (and so induced current) can be increased by either:
Increasing the speed of the movement — cutting more magnetic field lines in a given time.
Increasing the strength of the magnetic field (so there are more field lines that can be cut). ||| Generators and Microphones:
Generators make use of the generator effect to induce a current. Whether this current is alternating or direct all depends on two similar sounding methods of connection. Don’t get them mixed up.
||| Alternators Generate Alternating Current:
Alternators rotate a coil in a magnetic field (or a magnet in a coil).
Their construction is pretty much like a motor.
As the coil (or magnet) spins, a current is induced in the coil. This current changes direction every half turn.
Instead of a split-ring commutator, ac generators have slip rings and brushes so the contacts don’t swap every half turn.
This means they produce an alternating potential difference — more on this below. ||| Dynamos Generate Direct Current:
Dynamos work in the same way as alternators, apart from one important difference.
They have a split-ring commutator instead of slip rings.
This swaps the connection every half turn to keep the current flowing in the same direction (similar to the motion of a dc motor). ||| You Can Use an Oscilloscope To See the Generated pd:
Oscilloscopes show how the potential difference generated in the coil changes over time.
For ac this is a line that goes up and down, crossing the horizontal axis.
For dc the line isn’t straight like you might expect, but it stays above the axis (pd is always positive) so it’s still direct current.
The height of the line at a given point is the generated potential difference at that time.
Increasing the frequency of revolutions increases the overall pd, but it also creates more peaks too. ||| Microphones Generate Current From Sound Waves:
Microphones are basically loudspeakers in reverse.
Sound waves hit a flexible diaphragm that is attached to a coil of wire, wrapped around a magnet.
This causes the coil of wire to move in the magnetic field, which generates a current.
The movement of the coil (and so the generated current) depends on the properties of the sound wave (louder sounds make the diaphragm move further).
This is how microphones can convert the pressure variations of a sound wave into variations in current in an electric circuit.
Q: What is a microphone and how does it work to convert sound into electrical signals?
A: A microphone is a device that converts sound waves into electrical signals using the generator effect
also known as electromagnetic induction. In a moving-coil microphone
Q: Define the generator effect and explain how it induces a potential difference.
A: The generator effect
also known as electromagnetic induction
Q: Give examples of situations where the generator effect occurs.
A: Examples of the generator effect include:
Moving a wire through a magnetic field.
Moving a magnet into or out of a coil of wire.
Moving a magnet side to side in a coil to create brief current changes.
Rotating a magnet end-to-end inside a coil or rotating a coil within a magnetic field
as done in generators.
Q: How can the magnitude of an induced potential difference be increased?
A: The induced potential difference or current can be increased by:
Increasing the speed of motion of the magnet or conductor
which causes more magnetic field lines to be cut per second.
Increasing the strength of the magnetic field
creating more field lines for the conductor to cut.
Increasing the number of turns in the coil
allowing more of the conductor to interact with the magnetic field.
Q: What is electromagnetic induction and how is it related to the generator effect?
A: Electromagnetic induction is the production of a potential difference (voltage) when a conductor
such as a wire
Q: Explain how an alternating current (ac) generator
or alternator
A: An alternator is a type of generator that produces an alternating potential difference and current. It consists of a coil of wire rotating within a magnetic field
or a magnet rotating inside a coil. As the coil spins
Q: How can the output of an alternator be increased?
A: The output of an alternator can be increased by:
Increasing the rate of rotation of the coil.
Increasing the strength of the magnetic field.
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Energy Stores and Transfers, Open and Closed Systems36
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Examples of Energy Transfers, Energy Flow Diagrams13
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Calculation of Energy Changes, Conservation of Energy11
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Energy Dissipation, Reducing Unwated Energy Transfers in the Home13
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Conduction and Convection112
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Specific Heat Capacity, Intro to Thermal Conductivity22
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Required Practical: Specific Heat Capacity20
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Power124
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Required Practical: Investigating Insulation121
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Efficiency108
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Types of Energy Resources290
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Trends and Uses of Energy Resources, Energy for Transport and Heating246
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Charge and Current82
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Current, Potential Difference & Resistance58
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Required Practical: Investigating Resistance89
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Resistors and I-V Graphs132
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Required Practical: I-V Graphs99
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Series and Parallel Circuits55
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Direct and Alternating Current31
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Mains Electricity78
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Electrical Power25
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Electrical Energy Transfers and Power Ratings71
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The National Grid84
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Static Electricity and Sparks77
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Electric Fields and Sparks75
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Density - Intro13
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Required Practical: Density17
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States of Matter36
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Internal Energy35
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Specific Latent Heat, Heating & Cooling Graphs (and recap of Internal Energy)36
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Particle Motion in Gases, Gas Pressure & Temp, Boyle's Law, Work Done on Gases41
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Atomic Structure, Radioactive Decay, Types of Radiation, Intro to G-M Tube75
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Nuclear Equations, Half Life, Contamination, Irradiation, Peer Reviewing79
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Background Radiation, Correct Count-Rate, Uses and Risks of Radiation45
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Nuclear Fission and Fusion97
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Scalars and Vectors24
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Contact and Non-Contact Forces71
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Gravity, Weight & Centre of Mass97
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Resultant Forces, Scale Drawings, & Components of a Force113
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Work Done and Its Energy Transfers53
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Forces and Elasticity112
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Required Practical: Force and Extension118
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Moments, Levers and Gears101
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Pressure in Fluids118
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Upthrust and Atmospheric Pressure67
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Distance and Displacement17
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Speed and Velocity25
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Distance-Time Graphs24
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Acceleration106
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Velocity-Time Graphs61
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Terminal Velocity121
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Newton's First Law and Inertia61
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Newton's Second Law and Inertial Mass51
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Newton's Third Law73
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Required Practical: Force, Mass and Acceleration137
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Stopping Distance and How Braking Works131
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Momentum and Changes in Momentum104
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Vehicle Safety Features40
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Transverse & Longitudinal Waves36
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Wave Period & Speed, Measuring the Speed of Sound in Air23
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Required Practical: Measuring Waves in a Ripple Tank19
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Required Practical: Measuring Waves on a String9
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Sound Waves and Human Hearing101
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Using Ultrasound for Imaging and Detection70
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Using Seismic Waves for Exploration81
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Intro to Electromagnetic Waves, Intro to Visible Light92
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Uses of Radio Waves91
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Uses of Microwaves25
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Uses of Infrared Radiation33
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Uses of Visible Light21
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Uses of Ultraviolet Radiation25
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Uses of X-Rays and Gamma Rays27
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Dangers of Electromagnetic Waves63
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Visible Light and Colour Filters137
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Required Practical: Investigating Infrared Radiation75
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Reflection and Refraction114
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Specular and Diffuse Reflection61
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Required Practical: Reflection and Refraction119
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Lenses and Ray Diagrams153
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Black Body Radiation and Earth’s Temperature169
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Magnetism and Types of Magnets28
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Magnetic Fields30
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Electromagnetism, The Right Hand Grip Rule and Solenoids40
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The Motor Effect55
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Fleming's Left Hand Rule41
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Electric Motors and Loudspeakers25
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Induced Potential, The Generator Effect and Microphones52
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Transformers and their Equations137
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Our Solar System and Orbital Motion184
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The Life Cycle of Stars100
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Red Shift and The Big Bang81
