Edexcel GCSE Physics

Topic Questions

GCSEPhysicsEdexcelTopic Questions13. Electromagnetic Induction13.1 Electromagnetic Induction

13.1 Electromagnetic Induction

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1a
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Figure 1 shows a labelled transformer supplying homes in a village with electricity from a power cable.

7-3-e-1a-transformer-question

Figure 1

Complete the following sentences using words from the box. 

Each word can be used once, more than once or not at all.

cobalt direct input
secondary output primary
nickel iron alternating

 

     

Part W labels the input .............................. current.

Part X is the .............................. coil.

Part Y is the .............................. coil.

Part Z is made from .............................. .

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1b
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(i)
State the type of transformer shown in the diagram in part (a).
[1]
 
(ii)
Explain how the diagram shows this type of transformer.
[1]

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1c
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Compare the voltage in each coil of the transformer in the diagram in part (a).

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2a
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The national grid allows power to be efficiently delivered across the UK.
 


Describe where a step-up transformer is used as part of the National Grid.

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2b
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A teacher writes a note about a transformer but intentionally misses out some words.


Complete the following sentences using the correct words from the box.

  

coil core current
ends magnetic wire

 

     

A transformer works because an alternating .............................. in the primary .............................. produces a changing .............................. field in the ..............................  and then in the secondary coil.

This induces an alternating potential difference across the .............................. of the secondary coil.

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2c
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Explain why it is beneficial for the current in power cables to be small.

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3a
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Figure 1 shows a magnet passing through a coil of wire connected to an ammeter.

7-3-e-3a-generator-effect--

Figure 1

Explain why the ammeter shows a non-zero reading.

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3b
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A student moves the magnet towards the coil, from right to left. 



Describe the force they experience while moving the magnet.

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3c3 marks

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The student performs different actions and records the different ammeter readings they make for each action. 

Use statements from the box to describe the ammeter reading for each action. The first one has been completed for you. 

Needle doesn't move Needle moves to 0.8 A Needle moves to −0.4 A    

   

Action of student Reading on ammeter
Hold magnet still and move coil slowly towards magnet Needle moves to 0.8 A
Hold magnet still inside the coil
   		  
Move the magnet and coil together very quickly
   		  
Flip the magnet around and move slowly towards the coil  

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1a3 marks

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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.

 

fig-15-paper2h-june2020-edexcel-gcse-physics

Figure 1

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

[1]

fig-16-paper2h-june2020-edexcel-gcse-physics

Figure 1

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

[2]

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1b4 marks

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Figure 2 is a diagram representing a loudspeaker.

fig-17-paper2h-june2020-edexcel-gcse-physics

Figure 2

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

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1c4 marks

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Figure 3 shows a transformer.

fig-18-paper2h-june2020-edexcel-gcse-physics

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.
[3]

output voltage = .............................................................. V

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2a1 mark

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Which of these could be the output for a dynamo?
[1]

q9a-paper2h-june2018-edexcel-gcse-physics

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2b5 marks

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(i)
Figure 1 shows the output from a battery.
fig-17-paper2h-june2018-edexcel-gcse-physics
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.

[3]

potential difference = ............................................... V

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2c6 marks

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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.

P equals I squared cross times R

V subscript p cross times I subscript p equals V subscript s cross times I subscript s

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3a
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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.

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3b
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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?

13-1-h-3b-options-graph

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3c
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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.

13-1-h-3c-magnet-and-spring

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.

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3d
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Describe how the setup, from part c, can be altered to see a larger deflection on the voltmeter.

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1a4 marks
A student uses a plotting compass to investigate the magnetic field around a wire.

Figure 10 shows the wire going straight through a card.

compasses

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]
compasses-2
(ii)
Describe how the student could develop the investigation to find the shape of the magnetic field produced by the current.
[3]

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1b5 marks

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Figure 11 shows a copper wire between two magnetic poles.
                                                           
transformer
                                             

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     
[1]
square A down
square B up
square C towards the north pole of the magnet
square D towards the south pole of the magnet
                   
(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.
                                      
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]

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2a4 marks

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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]

  ☐ A twice the size of the current in the primary coil
  ☐ B half the size of the current in the primary coil
  ☐ C twice the size of the voltage across the primary coil
  ☐ D half the size of the voltage across the primary coil

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

[3]

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2b2 marks

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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 = ..............................................................

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2c6 marks

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

fig-19-paper2h-oct2021-edexcel-gcse-physics

Figure 19

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

fig-20-paper2h-oct2021-edexcel-gcse-physics

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.

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3a3 marks
Complete the following sentences using one of the phrases from the box below.
 
 
efficiency is reduced
the national grid
a power station
heat loss is reduced
a transformer

 

(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]

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3b1 mark
Which statement is true for transformers?


  ☐ A Transformers can only step-up voltages.
  ☐ B Transformers can only step-down voltages.
  ☐ C Transformers can work with direct current.
  ☐ D Transformers have primary and secondary coils.

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3c2 marks

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

I subscript s equals fraction numerator V subscript p cross times I subscript p over denominator V subscript s end fraction

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4a4 marks

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

7-2-h-3b-loudspeaker

Figure 1

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

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4b4 marks

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Use Figure 2 to explain how a microphone converts sound waves to alternating current.
13-1-m-4b-microphone-cross-section
Figure 2

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4c3 marks

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

7-3-h-3a-steam-generator

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. 

7-3-h-3a-p-d--trace

Figure 4

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

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4d2 marks

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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.

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5a3 marks

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

7-3-e-3a-generator-effect--

Figure 1

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

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5b1 mark

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

Describe any force the magnet experiences.

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5c4 marks

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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.

13-1-m-5c-thrown-magnet-coil

Figure 3
   

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

13-1-m-5c-current-vs-time-graph
Figure 4
   

Explain the shape of the graph.

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5d3 marks

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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.

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