Induced potential and the generator effect

The diagrams show a spring hanging from a nail.

• diagram 1 shows the spring with no weight added

• diagram 2 shows the spring stationary, after a weight has been added

• diagram 3 shows the spring after the weight has been pulled down

weight

Diagram 1
Diagram 2
Diagram 3

Which energy store has increased for the spring in diagram 2 compared to the spring in diagram 1?

The spring is released from the position shown in diagram 3.

Describe the energy transfers that take place until the spring stops vibrating.

Shock absorbers containing springs are used on motorcycles. Shock absorbers are designed to compress and expand as the motorcycle moves across a rough surface.

A new type of shock absorber has been developed to generate electricity from the movement of the motorcycle.

This new type of shock absorber consists of magnets that slide inside a coil when the motorcycle goes over a bump.

Some of the energy that would normally be wasted can be recovered, so fuel is saved.

Which of these statements best describes the advantage of this new type of shock absorber?

Explain how this new type of shock absorber can generate electricity.

Road X has a rough surface.

Road Y has a smooth surface.

(Source: © MikhailSh / Shutterstock)
(Source: © BearFotos / Shutterstock)

Road X
Road Y

A motorcycle travels at the same speed along road X and road Y.

Explain why the new type of shock absorber will generate more electricity for this motorcycle on road X than on road Y.

Diagram 1 shows a generator inside a small wind turbine. The generator is connected to a lamp and the windmill blades.

When the coil rotates in the direction of the arrow, the ammeter displays a small current.

Explain how the generator produces a current.

The generator in the wind turbine acts as an alternating current (a.c.) power supply.

Diagram 2 shows an electric circuit containing the generator being used to charge a mobile phone battery.

Direct current (d.c.) is needed to charge the battery.

Explain why there is a diode in the circuit.

Explain how the current in the battery will change if the wind speed increases.

The mean voltage across the battery is 7.2 V.

The battery gains 14 kJ of energy in 8400 seconds.

Calculate the mean current in the battery.

Diagram 1 shows some of the stages of electricity generation in a nuclear power station.

Nuclear fission takes place inside the reactor of the nuclear power station.

Give the name of a fuel that could be used in the reactor.

Energy is released from the fuel in the reactor by nuclear fission.

Describe the process of nuclear fission that takes place inside the reactor.

High pressure steam transfers energy from the reactor to a turbine.

The turbine spins as the steam passes through it.

Diagram 2 shows a simplified generator connected to the turbine.

Explain how electricity is generated by the generator.

At night the power station does not need to generate as much electricity.

Suggest how the output of this generator could be reduced.

The generator produces alternating current.

Describe the differences between alternating current (a.c.) and direct current (d.c.).

The diagram shows a step-down transformer.

The input power to the transformer is 16 W.

The transformer is used for 2.5 hours.

Calculate the energy transferred to the transformer during this time.

Explain how a transformer works.

In your answer, include reasons for using

• two coils

• the iron core

• an a.c. power supply

State how the primary coil of the transformer can be changed to increase the output voltage.

A device called a metal detector can be used to find metal buried underground.

The metal detector has two circuits, each containing a coil of copper wire.

Diagram 1 shows the circuit for the transmitter coil.

Suggest why there is a magnetic field around the transmitter coil.

The cell supplies direct current (d.c.). The electronics in diagram 1 change the direct current into alternating current (a.c.) in the coil.

Describe the difference between direct current (d.c.) and alternating current (a.c.).

Diagram 3 shows the circuit for the receiver coil.

As a result of the alternating current in the gold ring, there is an alternating current in the receiving coil.

Explain how an alternating current in the receiving coil causes a sound to be emitted from the loudspeaker.

The National Grid is used in the United Kingdom for the large-scale transmission of electricity. The photograph shows solar panels connected to the National Grid.

Solar panels provide direct current to a device that outputs an alternating current so that the energy from the solar panels can be supplied to the National Grid.

Explain why a step-up transformer is used to supply the National Grid.

This is the label on the step-up transformer.

State the formula linking input voltage, output voltage and turns ratio for a transformer.

Calculate the number of turns on the secondary coil of the step‑up transformer.

Solar panels produce constant direct current (d.c.).

Explain why a transformer will not work when connected to constant direct current.

Diagram 1 shows the magnetic field between the poles of two strong bar magnets.

Add labels to diagram 1 to show the poles of the bar magnets.

The bar magnets are made from steel.

Give one reason why steel is a good material for making bar magnets.

Explain how diagram 1 shows a uniform magnetic field.

Diagram 2 shows a metal wire being moved downwards through the uniform field between the poles of the same bar magnets. The orientation of the magnets has not been changed.

Give a reason why a voltage is induced between the ends of the metal wire as it moves between the poles of the bar magnets.

State two changes that could be made to this arrangement that would increase the magnitude of the induced voltage.

The diagrams show some equipment that the physicist Ørsted used in an investigation in 1820.

Diagram 1 shows the position of eight compass needles around a wire with no current in the wire.

The compass needles line up with and show the direction of the Earth’s magnetic field lines.

Diagram 2 shows the position of the same compass needles when a current is in the wire.

Diagram 2

Explain why the compass needles turn when the current is switched on.

Using evidence from the compass needles in diagram 2, draw on diagram 2 the shape and direction of a magnetic field line produced by the current in the wire.

Suggest what happens to the magnetic field when the current in the wire is reversed.

The current in the wire is turned off.

Diagram 3 shows the wire placed in a uniform magnetic field.

Diagram 3

The current is now switched on.

Draw an arrow to show the direction of the force on the wire.

The power supply in diagram 3 is replaced by an ammeter.

When the wire is moved, a current is detected.

Explain which direction the wire is moved in the magnetic field to produce a current in the wire.

Explain why a current is produced in the wire when the wire is moved in the magnetic field.

Diagram 1 shows a trolley seen from above.

A copper rod is attached to the front of the trolley.

The rod is connected to a voltmeter fixed to the trolley.

Diagram 2 shows the path of the trolley, backwards and forwards through a very strong magnetic field directed into the page.

The shaded area shows the magnetic field.

A voltage is induced in the copper rod as the trolley moves through the magnetic field.

Explain why the sign of the voltmeter reading changes as the trolley moves backwards and forwards.

Give a reason why the magnitude of the induced voltage might change.

The voltmeter is replaced by a resistor.

A charge of 1.410^–4C flows in the resistor during a time of 0.78 s.

Calculate the mean current in the resistor.

The thermal energy store of the resistor increases by 2.310^–6J as energy is transferred to it electrically.

Calculate the mean voltage across the resistor when a charge of 1.410^–4C transfers this energy.

Photograph 1 shows part of an ammeter that can measure very small currents.

A student moves a wire between the poles of a strong magnet and uses the ammeter to measure the induced current.

Determine the current reading shown by the ammeter in photograph 1.

Predict a value for the current if the movement of the wire was repeated with the poles of the magnet reversed.

Predict a value for the current if the wire is moved faster between the poles of the magnet.

Photograph 2 shows the structure of the ammeter. The ammeter has a needle attached to a coil of wire which can move freely around a magnet. When there is a current in the coil, the needle moves. The larger the current, the more the coil turns.

Suggest how the design of the ammeter could be modified to increase its sensitivity.

Photograph 3 shows part of the ammeter after a student has adjusted the ammeter in error.

The needle on the ammeter does not point to zero when there is no current.

Which of these factors has been decreased by the student’s adjustment?

Suggest how the student could correct the readings taken from this ammeter due to this error without adjusting the ammeter.

These equations may be required for both International GCSE Physics (4PH1) and International GCSE Combined Science (4SD0) papers.

4. Energy resources and energy transfers

The equations on the following page will only be required for International GCSE Physics.

These additional equations may be required in International GCSE Physics papers 2P

The diagram shows part of the National Grid.

There is a step-up transformer at the power station end of a transmission line and a step-down transformer at a distant town.

Explain why step-up transformers and step-down transformers are used in this way.

State the formula linking the input voltage, the output voltage and the turns ratio for a transformer.

The primary coil on a step-up transformer has 3300 turns.

Calculate the number of turns required on the transformer’s secondary coil to step up the voltage from 15 kV to 340 kV.

Transformers in the National Grid have efficiencies less than 100%.

Suggest which energy store of the transformer increases as a result of the efficiency being less than 100%.

The iron core of a transformer is an electrical conductor.

When the transformer is in use, the primary coil causes a changing magnetic field in the iron core. This causes a small current to be induced in the core.

Explain how a current is induced in the core of the transformer.

A racing car uses an engine and an electric motor to power its wheels.

The electric motor can only operate at maximum power for part of each lap of the race.

The electric motor has a maximum power output of 1.210⁵W.

The electric motor transfers 4.010⁶J of energy when it operates at maximum power.

Calculate the amount of time the electric motor can operate at maximum power.

The diagram shows a simplified view of a direct current (d.c.) electric motor.

State what is meant by the term direct current.

Explain the purpose of the brushes and the commutator in the d.c. motor.

The electric motor in the racing car can also be used as a generator to charge a battery pack. It is known as a motor generator unit (MGU).

The rotating wheels of the car cause the magnets in the MGU to spin near a coil of wire.

This induces a current in the coil when the coil is connected to the battery pack.

Name the energy store of the battery pack that increases when the battery pack is being charged.

Explain why the kinetic energy store of the car must decrease when the MGU charges the battery pack.

The diagram shows a torch that uses a rechargeable battery.

The battery is recharged by shaking the torch up and down.

(Source: adapted from © www.shutterstock.com/1328720216)

Shaking the torch causes the magnet to move up and down inside the coil of wire.

Explain why the movement of the magnet causes a current in the coil.

Using a stronger magnet could increase the current in the coil of wire.

State two other factors that could increase the current in the coil.

The diagram shows a bar magnet.

Draw four magnetic field lines around the bar magnet.

N S

The diagram shows a loop of wire connected to the terminals of a voltmeter.

Explain why the voltmeter reading changes from zero when the magnet is moved near the loop of wire.

This question is about a radio powered by a person turning a handle.

The radio has a battery which stores energy when the handle is turned.

The diagram shows the part of the radio called a generator.

The generator produces a voltage which does electrical work on the battery.

Explain how the generator produces a voltage.

The radio receives a radio wave of frequency 93 MHz.

State the formula linking speed, frequency and wavelength of a wave.

Calculate the wavelength of the radio wave.

[speed of radio waves 3.0 × 10⁸ m/s]

The signal received by the radio is converted into an alternating current (a.c.) signal.

Describe how the loudspeaker in the radio converts this a.c. signal into a sound wave.

State a modification that would increase the force on the loudspeaker coil.

This question is about bar magnets.

Describe an investigation to show the shape and direction of the magnetic field for a bar magnet.

You may draw a diagram to help your answer.

A bar magnet is used in a bicycle dynamo.

The diagram shows a cross-section of a bicycle dynamo.

The dynamo has a rotating wheel that presses against the tyre of the bicycle.

The rotating wheel is connected to a bar magnet by a spindle.

When the rotating wheel spins, the bar magnet spins.

The dynamo is connected to the lights on the bicycle.

Explain how the dynamo causes the lights to turn on when the bicycle is moving.

Suggest a disadvantage of using the dynamo to power the bicycle lights.

This question is about magnetic fields.

Diagram 1 shows a positively charged proton moving downwards in a uniform magnetic field.

magnetic field

Diagram 1

The proton experiences a force to the right.

What is the direction of the magnetic field?

When a current passes through a flat circular coil, a magnetic field is produced.

Complete diagram 2 by drawing the magnetic field of the flat circular coil.

Diagram 2

A wireless charging base uses a magnetic field to charge the battery of a mobile phone.

There is an alternating current in a coil of wire in the charging base.

There is another coil of wire connected to the battery in the mobile phone.

Explain how the wireless charging base charges the battery of the mobile phone.

Discuss the advantages and disadvantages of using a high current in the wireless charging base.