1. This question is about the magnetic effect of an electric current.
(i) Which one of the diagrams correctly shows the magnetic field caused by a wire conducting an electric
current (electric current flowing into the paper)?
______________ [1]
A wire is placed between the north and south poles of a permanent magnet and at right angles to the
magnetic field.
The current is switched on (electric current flowing into the paper). This creates a force on the wire in the
direction shown.
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(ii) Complete the diagram by labelling the North and South poles of the permanent magnet and sketching the
resulting magnetic field between the poles.
[2]
(iii) The current in the wire in (ii) is 0.2 A, and the magnetic flux density is 0.036 T.
Calculate the length of wire inside the magnetic field if the force experienced is 5.4 × 10–4 N.
______________ m [3]
2. Motors and generators both contain magnets and coils of wire.
Explain the similarities and differences between a motor and a generator.
The quality of written communication will be assessed in your answer.
[6]
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3(a). Lots of devices use an electric motor.
The diagram shows the main features of a motor.
The arrow on the diagram shows the force acting on side AB when a current flows in the coil.
(i) Draw another arrow on the diagram showing the force on side CD.
[1]
(ii) Why are there forces on sides AB and CD?
[2]
(b). Explain the function of the commutator in this motor.
[3]
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4(a). The diagram shows part of a loudspeaker. It contains specially-shaped permanent magnets with south poles, S,
in a ring around the outside and a circular north pole, N, in the centre.
In the gap between the shaped magnets there is a circular coil carrying electrical current.
The direction of the magnetic field between the poles is shown as .
The magnetic field through the coil has strength 0.40 T.
The coil has circumference 25 mm and has 200 turns. The diagram shows only 3 turns of this coil.
A clockwise current of 0.60 A in the coil produces a force on the coil.
What is the direction of the force on the coil?
Tick (✓) one box.
Anti-clockwise
Clockwise
Into the page
Out of the page
[1]
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(b). Calculate the magnitude of the force acting on the coil.
Force = ............................................... N [4]
END OF QUESTION PAPER
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Mark Scheme
Question Answer/Indicative content Marks Guidance
1 i B 1
ii N and S pole correctly labelled (1) 2
Magnetic field pattern correct direction
between poles and over the top of the wire
(1)
iii FIRST CHECK THE ANSWER ON 3
ANSWER LINE
If answer = 7.5 × 10–2 (m) award 3 marks
Select F = BIL
Rearrange to get L = F ÷ (BI) (1)
5.4 × 10–4 N ÷ (0.036 × 0.2) (1)
7.5 × 10–2 (m) (1)
Total 6
2 (Level 3) 6 This question is targeted at grades up to A
Detailed descriptions of the generator and Indicative scientific points:
the motor. Some correct comparison of the Motor:
two. Quality of written communication does
not impede communication of the science electricity / current produces rotation
at this level. uses direct current
attempt to describe use of commutator.
(5–6 marks)
Generator:
(Level 2) rotation of coil produces electricity
Brief description of how a motor works and no need for commutator / explains slip
how a generator works or a more detailed rings
description of either one. Quality of written example shown produces alternating
communication partly impedes current
communication of the science at this level. reference to power station / dynamo
etc.
(3–4 marks)
Both:
(Level 1) (stationary) magnetic field
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Mark Scheme
Question Answer/Indicative content Marks Guidance
Brief description of how a motor works or rotating coil
how a generator works. May be some difference between ac and dc
confusion of difference between them. graphs of ac and dc.
Quality of written communication impedes
communication of the science at this level. Accept
higher level answers regarding interaction
(1–2 marks) of magnetic field and current.
Use the L1, L2, L3 annotations in Scoris;
(Level 0) do not use ticks.
Insufficient or irrelevant science. Answer
not worthy of credit. Examiner's Comments
(0 marks)
This was a challenging six-mark extended
writing question. The majority of
candidates scored 0 marks on this
question. The best responses took time to
carefully describe how a motor works,
using appropriate technical terms, before
doing the same for a generator, then finally
comparing the two. The majority of the
candidates that scored any marks did so
for a basic description of a generator as a
rotating/moving coil (or magnet) producing
electricity in the coil, although many also
confusingly described a motor as a
generator, therefore restricting their
performance to level one. Even basic
knowledge of the workings of a motor, as
demonstrated here was extremely limited,
and technical details such as the
commutator for the motor and/or slip rings
for the generator were seen in only a
minority of responses. The correct use of
the term induction was occasionally seen
in reference to the generator, but also
incorrectly in reference to the motor.
Total 6
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Mark Scheme
Question Answer/Indicative content Marks Guidance
3 a i downwards arrow 1 needs to be near CD
Examiner's Comments
Most candidates drew a clear vertical
arrow downwards. A small number drew it
too far away from side CD.
ii current / moving charge / moving electrons 2 not induced / creates current
(in wires) (1) allow magnetic field around the wire
(produced by the current)
(in) magnetic field (1) allow between magnets / poles
ignore N and S
Examiner's Comments
Some answers confused the motor with a
generator and others misunderstood what
the question was asking as their answers
gave the purpose of the forces to turn the
coil. Magnets were quite often mentioned
but not the magnetic field. Many answers
lacked clarity and the use of the
appropriate scientific terminology. Some
candidates described the forces as an
interactive pair.
b any THREE from: 3 Examiner's Comments
allows coil / motor to spin / rotate Less than half the candidates achieved any
marks on this part. There was confusion
without tangling the wires again with a generator. Vague references
were made to something changing
allows current to flow (in / out of coil) direction, though some thought it was the
coil or the magnets. Very few candidates
reverses direction of current gave a clear and full description of the
function of the commutator.
reverses direction of the coil's magnetic
field
keeps forces on coil in same direction
every half turn / each time coil passes
vertical
Total 6
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Mark Scheme
Question Answer/Indicative content Marks Guidance
4 a Out of the page ✓ 1 Examiner’s Comments
(AO 1.2)
Candidates needed to be able to recall and
apply Fleming’s left hand rule. At every
position, the direction of the current is
perpendicular to the magnetic field and so
the force or thrust or motion indicated by
the thumb is out of the page.
b FIRST CHECK THE ANSWER ON 4 ALLOW 3 marks if 200 turns omitted,
ANSWER LINE 0.0060 N
If answer = 1.2 (N) award 4 marks
ALLOW 3 marks if using 5000mm, 1200N
select force = magnetic flux density × (AO 1.2)
current × length of conductor ✓ ALLOW 2 marks if 200 turns omitted and
no conversion of 25mm to m, 6N
calculate length correctly, including unit (AO 2.2)
conversion length = 0.025 × 200 = 5 (m) ✓ ALLOW 1 mark for a substitution that
shows evidence of the formula
= 0.40 × 0.60 × 5 ✓ (AO 2.1) Also gains m.p.1 and m.p.2
= 1.2 (N) ✓ (AO 2.1) Examiner’s Comments
Most candidates were able to select the
correct formula but then failed to calculate
the length of the conductor with a correct
unit conversion.
Total 5
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