Electromagnetic Induction (Edexcel GCSE Physics): Exam Questions

A student uses a plotting compass to investigate the magnetic field around a wire.

Figure 10 shows the wire going straight through a card.

Figure 10 shows the compass needle when there is no current in the wire.

(i) Which of these shows a possible direction of the compass needle when there is a current in the wire going from P to Q?

[1]

(ii) Describe how the student could develop the investigation to find the shape of the magnetic field produced by the current.

[3]

Higher Tier Only

Figure 11 shows a copper wire between two magnetic poles.

The current in the wire is in the direction shown by the arrow.

The wire experiences a force due to the magnetic field.

(i) The direction of the force due to the magnetic field is

A down

B up

C towards the north pole of the magnet

D towards the south pole of the magnet     

[1]

(ii) The interaction between the magnetic fields produced by the magnet and the current in the wire produces forces on the magnet and the wire.

Compare these two forces.

[1]

(iii) Figure 12 shows a different wire inside a uniform magnetic field.

The magnetic flux density of the magnetic field is 0.72 N/A m.

The length of the wire inside the field is 30 mm.

The size of the force due to the magnetic field on the wire is 0.045 N.

Calculate the size of the current in the wire.

Use an equation selected from the list of equations at the end of this paper.

[3]

Higher Tier Only

There is an alternating current of 3 A in the primary coil of a transformer.

There is an alternating current of 6 A in the secondary coil of the transformer.

The transformer is 100% efficient.

i) The size of the potential difference (voltage) across the secondary coil is

[1]

ii) Explain how an alternating current in the primary coil causes an alternating current in the secondary coil of the transformer.

[3]

Higher Tier Only

The primary coil of a different transformer is connected to the 230 V mains supply.

The voltage across the secondary coil is 15 V. The primary coil has 600 turns.

Calculate the number of turns on the secondary coil.

Use an equation selected from the list of equations at the end of the paper.

number of turns = ..............................................

Higher Tier Only

Figure 19 shows a coil of wire that is being rotated between the poles of a magnet.

Figure 19

Figure 20 shows how the current in the coil changes during one complete rotation of the coil.

Figure 20

Explain why the current changes in the way shown by the graph in Figure 20.

Your answer should include details of the position of the coil relative to the magnet at each of the times labelled P, Q, R, S and T.

You may use diagrams to help your answer.

Complete the following sentences using one of the phrases from the box below. 

(i) Electrical power is generated at .............................................

[1]

(ii) Electricity is transmitted over long distances by transmission

lines that are part of.............................................................

[1]

(iii) Electricity is transmitted at high voltages so that......................

[1]

Which statement is true for transformers?

In a small transformer

• the primary voltage is 230 V

• the primary current is 0.020 A

• the secondary voltage is 5.0 V

Calculate the secondary current.

Use the equation

Higher Tier Only

Figure 1 shows a diagram of a loudspeaker in a live music venue.

Figure 1

Explain why an alternating current in the coil causes the speaker cone to oscillate.

Higher Tier Only

Use Figure 2 to explain how a microphone converts sound waves to alternating current.

Figure 2

Higher Tier Only

A similar effect occurs in power stations. Steam from water heated by fuels turns a turbine - this generates electricity, as shown in Figure 3.

Figure 3

Figure 4 is an oscilloscope trace of the potential difference in the coil in Figure 3. The vertical axis is potential difference and the horizontal axis is time. 

Figure 4

Referring to the apparatus in Figure 3, explain the shape of the potential difference graph in Figure 4.

Higher Tier Only

The volume of steam passing the turbine per second halves, causing its rotational period to double.

Sketch the new trace on the oscilloscope in Figure 4.

Higher Tier Only

Figure 1 shows a magnet passing through a coil of wire connected to an ammeter.

Figure 1

Explain why the ammeter's reading changes from 0 Amps.

Higher Tier Only

A student moves the magnet towards the coil's right hand side.

Describe any force the magnet experiences.

Higher Tier Only

A student throws a magnet up through a coil of wire attached to a digital ammeter.

Three different stages of this motion are shown in Figure 3.

Figure 3   

The current-time graph from the digital ammeter is shown in Figure 4.

Figure 4

Explain the shape of the graph.

Higher Tier Only

The magnet is thrown again at the same initial velocity, but this time with the north pole pointing upwards.

On Figure 4, sketch the new graph of current against time.

Figure 10 shows part of the National Grid linking a power station to homes.

Figure 10

Which row in the table describes the transformers at X and Y?

Explain why electricity is transmitted at a high voltage through the National Grid.

Transformers are used to connect household appliances to the mains electricity supply.

The input voltage to the transformer is .

The input current to the transformer is .

The transformer has an output voltage of .

The transformer used is 100% efficient.

Calculate the output current of the transformer.

Use the equation

This question is about transformers.

A phone charger contains a transformer. The charger is plugged into the mains supply and produces an output voltage of to charge a phone.

State whether the transformer in the charger is a step-up or a step-down transformer.

Give a reason for your answer.

The primary coil of the transformer has turns.

Calculate the number of turns on the secondary coil.

Use the equation:

The transformer is 100% efficient. The current drawn from the mains supply is .

Calculate the output current of the transformer.

Use the equation:

Higher Tier Only 

Figure 1 shows three stages of a magnet moving into and then out of a coil of wire. The coil is connected to a milliammeter.

Figure 1

(i) Which row of the table shows the deflection on the milliammeter for the three stages in Figure 1?

Figure 1

[1]

(ii) Give two ways of increasing the deflections on the milliammeter shown in Figure 1.

[2]

Higher Tier Only 

Figure 2 is a diagram representing a loudspeaker.

Figure 2

Explain how sound is produced when an alternating current is supplied to the coil of the loudspeaker.

Higher Tier Only

Figure 3 shows a transformer.

Figure 3

(i) State the purpose of the transformer shown in Figure 3.

[1]

(ii) Calculate the output voltage of the secondary coil.

Use an equation selected from the list of equations at the end of this paper.

output voltage = .............................................. V[3]

Higher Tier Only

Which of these could be the output for a dynamo?

Higher Tier Only

(i) Figure 1 shows the output from a battery.

Figure 1

Explain why a transformer will not work with the input current as shown in Figure 1.

[2]

(ii) A transformer has 30 turns on the primary coil and 150 turns on the secondary coil.

A potential difference of 25 V is applied across the primary coil.

Calculate the potential difference across the secondary coil.

Use an equation selected from the list of equations at the end of this paper.

potential difference = ............................................... V[3]

Higher Tier Only

High voltage transmission cables and transformers are used in the national grid.

Explain how using high voltage transmission cables and transformers allows the distribution of electrical power around the United Kingdom to be as efficient as possible.

Refer to the following equations in your answer.

Higher Tier Only

A step-up transformer is placed outside a building.

It has 50 turns on its primary coil with an input power of 160 kW and an input current of 40 A. The output current is 20 A. 

Calculate the number of turns in the secondary coil of the transformer.

Higher Tier Only

Opening the switch in a circuit produces the opposite magnetic effect to closing the switch.

A student connected a switch, a fixed resistor and a battery to the primary coil. A fixed resistor is also connected to the secondary coil. 

The circuit is switched closed, then opened 10 seconds later.

 Which graph best represents the current in the secondary circuit?

Higher Tier Only

Figure 1 shows the setup a student is using to generate an alternating voltage, which is seen by the deflection of the arrow on the voltmeter.

Figure 1

The coil is held stationary on a bench whilst the magnet can move freely inside it.

Explain how this setup produces an alternating potential difference.

Higher Tier Only

Describe how the setup, from part c, can be altered to see a larger deflection on the voltmeter.

Figure 12 shows two stages of a magnet moving into a coil of wire. The coil is connected to a centre-zero sensitive ammeter.

Figure 12

In stage 1, there is a deflection on the ammeter as the magnet moves into the coil.

In stage 2, the magnet is held stationary inside the coil.

What does the ammeter show in stage 2?

State two changes that would increase the size of the deflection on the ammeter.

When the magnet is pulled back out of the coil, the ammeter shows a deflection in the opposite direction.

Explain why the deflection on the ammeter changes direction when the magnet is pulled out of the coil.

A loudspeaker and a microphone both contain a coil of wire near a permanent magnet.

Compare how the loudspeaker and the microphone operate.

Your answer should explain:

• how each device converts energy from one form to another

• the role of the coil and the magnet in each device