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A LevelPhysicsCIEExam Questions20. Magnetic Fields20.2 Electromagnetic Induction

Syllabus Edition

First teaching 2020

Last exams 2024

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Electromagnetic Induction (CIE A Level Physics)

Exam Questions

1 hour6 questions
Easy
Medium
1a
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State Faraday's Law  

(i)
in words
[2]
(ii)
as an equation, defining all the quantities.
[2]

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1b
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Lenz’s law is sometimes combined with Faraday’s law in order to explain electromagnetic effects. 

Use the words below to complete the description of Lenz's law

 
attracts        opposes        density        direction        linkage        magnitude

 

The _________ of an induced emf is always set up in a way such that it  ________ the change in magnetic flux ___________ that causes it. 

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1c
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Rewrite the equation you wrote in (a)(ii) to include Lenz's law.

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1d
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A small coil of wire connected to a sensitive voltmeter is placed near one end of a solenoid (in which an electrical current is flowing) as shown in Fig. 1.1.

20-2-1d-e-20-2-e-solenoid-coil-em-induction-cie-ial-sq

Fig. 1.1

State two different ways in which an e.m.f. may be induced in the coil.

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2a
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(i)
Define magnetic flux.
[2]
(ii)
Write the equation for magnetic flux when the magnetic flux density is not perpendicular to the area.
[1]

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2b
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A circular coil with an area of 0.1 m2 and 500 turns is placed with its plane perpendicular to a horizontal magnetic field of uniform flux density 80 mT as shown in Fig. 1.1.

20-2-2b-e-20-2-e-circular-coil-em-induction-cie-ial-sq

Fig. 1.1

Calculate the magnetic flux passing through the coil. Give a unit with your answer.

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2c
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The coil experiences a change in magnetic flux linkage when it is rotated through 90° about a vertical axis (indicated in Fig. 1.1).

(i)
Define magnetic flux linkage
[1]
(ii)
Calculate the change in magnetic flux linkage produced by the rotation of the coil.
[2]

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2d
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The coil rotates through 90° in a time of 300 ms.

Calculate the average magnitude of the induced e.m.f. in the coil during the rotation.

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3a
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Table 1.1 shows the standard international (SI) units of the main quantities involved in electromagnetic induction.

Table 1.1

Quantity

Symbol

SI unit

magnetic flux

ϕ

 

magnetic flux linkage

 

Wb turns

electromotive force

  

 
 

B

 

 

Complete Table 1.1 by filling in the missing quantities, symbols and SI units.

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3b
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A coil is connected to a voltmeter, which is centred at zero as shown in Fig. 1.1a.

20-2-3b-e-20-2-e-coil-magnet-voltmeter-experiment-cie-ial-sq

Fig. 1.1a

When the magnet is lowered into the coil, the needle on the voltmeter deflects to the right as shown in Fig. 1.1b.

qu1c-fig-1b

Fig. 1.1b

On Fig. 1.1c, sketch the expected observations of the voltmeter needle when

 

(i)
the magnet is held at rest in the coil
[1]
(ii)
the magnet is removed from the coil faster than it entered
 

qu1c-fig-2

Fig. 1.1c

[3]

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3c
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The magnet is moved towards and away from the coil at a steady rate.

Fig. 1.2 shows the variation of time with the reading of potential difference on the voltmeter.

alternator-graph

Fig. 1.2

Use Fig. 1.2 and Faraday’s law to explain why

 
(i)
there is a reading on the voltmeter,
[1]
(ii)
this reading varies in magnitude,
[2]
(iii)
the reading has both positive and negative values.
[2]

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3d
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As the magnet is moved away from the coil, the voltmeter shows a value of 1.5 mV for 2.0 s.

Calculate the change in magnetic flux linkage as the magnet is moved away from the coil.

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1a
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(i)
Define magnetic flux.

[2]

(ii)
State Faraday’s law of electromagnetic induction.

[2]

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1b
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A solenoid has a coil C of wire wound tightly about its centre, as shown in Fig. 7.1.

q7b-paper-4-specimen-2022-cie-ial-physics

Fig. 7.1

The coil C has 96 turns.
The uniform magnetic flux Φ, in Wb, in the solenoid is given by the expression

Φ = 6.8 × 10–6 × I

where I is the current, in A, in the solenoid.

Calculate the average electromotive force (e.m.f.) induced in coil C when a current of 3.5 A is reversed in the solenoid in a time of 2.4 ms.



e.m.f. = ................................... V 

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1c
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The d.c. supply in Fig. 7.1 is now replaced with a sinusoidal alternating supply.

Describe qualitatively the e.m.f. that is now induced in coil C.

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2a
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A small solenoid of area of cross-section 1.2 × 10−3 m2 is placed inside a larger solenoid of area of cross-section 7.8 × 10−3 m2, as shown in FIg. 1.1

20-2-2a-m-small-and-large-solenoids-sq-cie-a-level

Fig. 1.1

The larger solenoid has 800 turns and is attached to a d.c. power supply to create a magnetic field.

The smaller solenoid has 2000 turns.

Compare the magnetic flux in the two solenoids.

 

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2b
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Compare the magnetic flux linkage in the two solenoids.

 

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2c
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State Lenz's Law of electromagnetic induction.

 

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2d
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The terminals of the smaller solenoid are connected together. The smaller solenoid is then removed from the inside of the larger solenoid. 

With reference to magnetic fields, explain why a force is needed to remove the smaller solenoid. 

 

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3a
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Define magnetic flux linkage. 

 

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3b
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A square coil of wire of side length 10 cm consists of 5 insulated turns. The coil is stationary in a uniform magnetic field. The plane of the coil is perpendicular to the magnetic field, as shown in Fig. 1.1.

 
20-2-3b-m-square-coil-sq-cie-a-level
Fig. 1.1
   
The flux density B of the magnetic field varies with time t as shown in Fig. 1.2.
 
20-2-3b-m-flux-density-graph-sq-cie-a-level
Fig. 1.2
 
Determine the magnetic flux linkage inside the coil at time t = 0.30 s. Give a unit with your answer.
 
magnetic flux linkage = ............................... unit ................ 

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3c
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(i)
State how the graph in Fig. 1.2 shows that the e.m.f. induced across the terminals between t = 0 and t = 0.30 s is constant. 
[1]
 
(ii)
Calculate the magnitude of the e.m.f.
 
e.m.f = ............................................................. V [2]

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3d
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The procedure in (b) is repeated, but this time the terminals of the coil are connected together. 

State and explain the effect on the coil of connecting the terminals together during the change of magnetic flux density shown in Fig. 1.2.

 

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