M OIZ DAWO ODI

O’ LEVEL
O / A L EVEL P HYSI C S

PHYSICS
Electromagnetic Effects

4.5
ST UD E N T N A M E

PHYSICS WITH
MOIZ DAWO ODI
O'Levels

4.5 Electromagnetic Effects

 4.5.1 Electromagnetic Induction

Simulation https://phet.colorado.edu/sims/html/faradays-
Link law/latest/faradays-law_en.html
4.5.2 e A.C Generator

N S
4.5.3 Magnetic Effect of a Current
4.5.4 Forces on a Current-Carrying Conductor
4.5.5 e D.C. Motor

N S

N S
4.5.6 e Transformer
Match the following
 P 1 Past Papers
01 The diagram shows three pairs of parallel wires with the currents in the directions shown.

X Y Z

For each pair of wires, what are the forces between the wires?

X Y Z

A attraction none repulsion

B attraction repulsion attraction
C repulsion attraction repulsion
D repulsion repulsion repulsion [MJ2011/P11/Q33]

02 The coil in an electric motor is wound onto a cylinder.

Why is the cylinder made of soft iron?

A to deflect the magnetic field away from the coil

B to increase the current through the coil
C to increase the strength of the magnetic field through the coil
D to support the coil and prevent it from collapsing [MJ2011/P11/Q34]

03 The electromotive force (e.m.f.) induced in a conductor moving at right-angles to a magnetic field
does not depend upon

A the length of the conductor.

B the resistance of the conductor.
C the speed of the conductor.
D the strength of the magnetic field.
[MJ2011/P11/Q35]
04 The diagram shows part of an a.c. generator when its coil is in a horizontal position.

magnet coil

N S

The graph shows the voltage output plotted against time.

Which point on the graph shows when the coil is in a vertical position?

A
voltage
output D

B
0
0 time

C
[MJ2011/P11/Q35]

05 The diagram shows an alarm system.

battery P
iron core

iron armature

pivot

bell

What happens when battery P is disconnected?

iron armature bell

A falls rings
B falls stops ringing
C moves up rings
D moves up stops ringing [ON2011/P11/Q25]
06 Two parallel wires carry currents in the same direction.
Which diagram shows the magnetic field around each wire and the direction of the force on each
wire?

A B

currents currents
magnetic magnetic
fields fields

forces forces

C D

currents currents
magnetic magnetic
fields fields

forces forces
[ON2011/P11/Q34]

07 The diagrams show three electrical devices, X, Y and Z.

coil rotation soft iron

N rotation
rotation N
axis
coil N S S

S cylindrical
magnet coil

X Y Z

Which devices provide an alternating current (a.c.) output?

A X only B Y only C X and Y D X and Z [ON2011/P11/Q35]

08 One component of a simple d.c. motor is a split-ring commutator.
Which metal is used to make the commutator, and why is this metal chosen?

metal reason

A copper it is a good conductor of electricity

B copper it is a good conductor of heat
C iron it increases the magnetic field strength
D iron it is attracted to the brushes [ON2011/P11/Q36]

09 A small coil is connected to a galvanometer G, as shown.

When a magnet is allowed to fall towards the coil, the galvanometer pointer gives a momentary
deflection to the right of the zero position.

The magnet moves through the coil.

What happens to the galvanometer pointer as the magnet falls away from the coil?

A It gives a continuous reading to the left.

B It gives a momentary deflection to the left.
C It gives a continuous reading to the right.
D It gives a momentary deflection to the right. [ON2011/P11/Q37]
10 Two straight electrical conductors are parallel to one another. Each carries a current, one into the
plane of the paper and one out of the plane of the paper.
Which diagram shows the magnetic field around the two wires?

A B

key
current into
plane of paper
C D
current out of
plane of paper

[MJ2012/P11/Q26]

11 A current-carrying wire is placed between the poles of a magnet.

What is the direction of the force on the wire due to the current?

N D B S

C
[MJ2012/P11/Q33]

12 A simple d.c. motor consists of a coil that rotates between the poles of a permanent magnet. The
turning effect is increased by winding the coil on a metal cylinder.
Which metals are used to make the magnet and the cylinder?

magnet cylinder

A iron copper
B iron steel
C steel copper
D steel iron [MJ2012/P11/Q34]
13 A current is produced when a wire is moved between two magnets as shown.

ammeter A

N S

movement
of wire

Which device uses this effect?

A a battery
B a generator
C a motor
D an electromagnet [MJ2012/P11/Q35]

14 Why is a transformer used to connect a generator in a power station to a long-distance

transmission line?
A to decrease the voltage and decrease the current
B to decrease the voltage and increase the current
C to increase the voltage and decrease the current
D to increase the voltage and increase the current [MJ2012/P11/Q36]
15 Two long, straight wires hang vertically, close to each other.
The wires carry currents in opposite directions.

current current
out of page into page

Which diagram shows the magnetic field pattern around the wires?

A B

C D

[MJ2012/P12/Q26]

16 The diagram shows a beam of electrons entering a magnetic field. The direction of the field is into
the page.

magnetic field
be am of electrons into page

In which direction are the electrons deflected?

A into the page

B out of the page
C towards the bottom of the page
D towards the top of the page [MJ2012/P12/Q33]
17 A rectangular coil is placed between the poles of a magnet. A current passes through the coil, as
shown.

N S

What happens to the coil?

A It moves downwards.
B It moves upwards.
C It rotates anticlockwise.
D It rotates clockwise.

18 A bar magnet is pushed into one end of a long coil connected to a sensitive meter.
bar magnet coil

[MJ2012/P12/Q34]

sensitive meter

Which of the following affects the magnitude of the deflection of the meter?

A the direction in which the coil is wound

B the speed with which the magnet enters the coil
C which end of the coil is used
D which pole of the magnet enters first [MJ2012/P12/Q35]

19 Which graph represents the voltage output of a simple a.c. generator?

A B

voltage voltage

0 0
0 time 0 time

C D

voltage voltage

0 0
0 time 0 time

[MJ2012/P12/Q36]
20 A vertical wire passes at right angles through a piece of card. There is a large current in the wire
in the direction shown.
direction of
current in wire

card

plotting
compass

A plotting compass is placed on the card.

Which diagram shows the direction in which the needle of the plotting compass points?

A B C D

[ON2012/P11/Q26]

21 Each of the diagrams shows a cross-section through two parallel, current-carrying conductors.
Which diagram shows the shape of the magnetic field pattern and the directions of the forces on
the two conductors?

key
A conductor carrying current into page
conductor carrying current out of page

D
[ON2012/P11/Q33]
22 The diagram shows a simple d.c. motor.

What is the part labelled Q?

A a coil
B a magnet
C a slip ring
D a split-ring commutator [ON2012/P11/Q34]

23 The diagram shows the N-pole of a magnet moving into, and out of, a coil of wire.

N X coil of wire
magnet

This movement produces a current in the coil of wire. The current produces a magnetic pole at X.

Which pole is produced at X when the magnet is moved in and when it is moved out?

magnet moved in magnet moved out

A N N
B N S
C S N
D S S [ON2012/P11/Q35]
24 A simple a.c. generator produces an alternating e.m.f. as shown.
1.0

e.m.f. / V 0
0 1.0 2.0 time / s
_ 1.0

The speed of the generator is doubled.

Which graph best represents the new output?

1.0

A e.m.f. / V 0
0 1.0 2.0 time / s
_ 1.0

2.0

1.0

B e.m.f. / V 0
0 1.0 2.0 time / s
_ 1.0

_ 2.0

1.0

C e.m.f. / V 0
0 1.0 2.0 time / s
_ 1.0

2.0

1.0

D e.m.f. / V 0
0 1.0 2.0 time / s
_ 1.0

_ 2.0
[ON2012/P11/Q36]

25 What is required to operate a reed relay in a switching circuit?

A a capacitor
B an electric field
C a magnetic field
D a transformer [ON2012/P11/Q37]
26 Two parallel wires carry currents in opposite directions. Three plotting compasses are placed in
the positions shown.

[ON2012/P12/Q33]

The currents in both wires are reversed. How many compass needles change direction?
(Ignore the effect of the Earth’s magnetic field.)

A 0 B 1 C 2 D 3

27 Which single-coil motor has the largest turning effect?

number of turns
current in coil / A iron core
in coil

A 6 100 no
B 10 200 no
C 6 100 yes
D 10 200 yes [ON2012/P12/Q34]

28 A magnet is moved towards a coil of insulated wire. A voltmeter connected across the coil shows
a positive reading.

What produces a higher reading on the voltmeter?

A moving the magnet away from the coil at the same speed
B moving the magnet away from the coil at a slower speed
C moving the magnet towards the coil at a faster speed

[ON2012/P12/Q35]
D moving the magnet towards the coil at a slower speed
29 A wire hangs between the poles of a magnet.
When there is a current in the wire, in which direction does the wire move?

current
in wire
N

C
B
D
A S

[MJ2013/P11/Q34]

30 The diagram shows a simple d.c. motor.

Which labelled part is the commutator?
A

D [MJ2013/P11/Q35]

31 Two leads emerging from a box are connected to a sensitive ammeter.

bar magnet ammeter

When a bar magnet moves towards the open end of the box, the needle of the ammeter deflects
to the right. When the bar magnet stops, the needle returns to zero.

What is inside the box?

A a coil alone
B a coil connected in series with a cell
C a light-dependent resistor (LDR) alone
D an LDR in series with a cell [MJ2013/P11/Q36]
32 The diagram shows the shape of the magnetic field lines near a current-carrying conductor.

conductor

P
Q

The current in the conductor is into the plane of the diagram.

Which row correctly states the direction of the field lines and compares the strengths of the field
at points P and Q?

direction of field lines the field is stronger at

A clockwise P
B clockwise Q
C anticlockwise P
D anticlockwise Q [ON2013/P11/Q25]

33 A transformer is used to operate a 12 V lamp from a 250 V mains supply.

transformer

250 V 12 V
0.10 A 2.0 A

The mains current is 0.10 A. The current in the lamp is 2.0 A.

What is the efficiency of the transformer?

[ON2013/P11/Q31]
A 0.048 B 0.050 C 0.96 D 1.04
34 A current-carrying wire lies between the poles of two magnets, as shown.
wire direction
of current

N S

What is the direction of the force on the wire?

A into the plane of the paper

B out of the plane of the paper
C towards the N-pole
D towards the S-pole [ON2013/P11/Q32]

35 Which material is used for the core of a transformer and why?

material reason

A copper good conductor of electricity

B copper easy to magnetise and demagnetise
C iron good conductor of electricity
D iron easy to magnetise and demagnetise [ON2013/P11/Q34]
36 The graph shows the output of an a.c. generator. The coil in the generator rotates 20 times in one
second.
+1
output
p.d. / V 0
0 0.05 0.10 time / s
–1

The speed of rotation of the coil steadily increases.

Which graph best shows how the output changes?

+1
output
A p.d. / V 0
0 0.05 0.10 time / s
–1

+1
output
B p.d. / V 0
0 0.05 0.10 time / s
–1

+2
output
p.d. / V
+1

C 0
0 0.05 0.10 time / s
–1

–2

+2
output
p.d. / V
+1

D 0
0 0.05 0.10 time / s
–1

–2

[ON2013/P11/Q33]
37 The diagram shows a wire placed between two magnetic poles of equal strength.
A current passes through the wire in the direction shown. The current causes a downward force
on the wire.

wire

direction
of force
direction
of current

What is the arrangement of the magnetic poles?

S N
A

N S
B

N N
C

S S
D

[ON2013/P12/Q32]
38 The graph shows the output of an a.c. generator. The coil in the generator rotates 20 times in one
second.
+1
output
p.d. / V 0
0 0.05 0.10 time / s
–1

The speed of rotation of the coil steadily increases.

Which graph best shows how the output changes?

+1
output
A p.d. / V 0
0 0.05 0.10 time / s
–1

+1
output
B p.d. / V 0
0 0.05 0.10 time / s
–1

+2
output
p.d. / V
+1

C 0
0 0.05 0.10 time / s
–1

–2

+2
output
p.d. / V
+1

D 0
0 0.05 0.10 time / s
–1

–2 [ON2013/P12/Q33]
39 A beam of alpha-particles enters the magnetic field between the poles of a magnet.

alpha-particles

In which direction is the magnetic force on the beam?

A down the page

B into the page
C out of the page
D up the page [MJ2014/P11/Q34]

40 As a magnet is moved into the coil of wire as shown, there is a small reading on the sensitive
ammeter.

N S

Which change increases the size of the reading?

A moving the opposite pole into the coil

B pulling the magnet out of the coil
C pushing the magnet in faster
D unwinding some of the turns of wire [MJ2014/P11/Q35]
41 An ideal transformer has a primary voltage of 600 V and a secondary voltage of 240 V.

The secondary coil is attached to a resistor of resistance 120 Ω.

primary coil secondary coil

600 V 240 V 120 Ω

What is the power dissipated in the resistor and the current in the primary coil?

power / W current / A

A 120 0.20
B 120 5.0
C 480 0.80
D 480 1.3 [MJ2014/P11/Q36]

42 Which device uses the force experienced by a current in a magnetic field when in normal use?
A cathode-ray oscilloscope
B electrostatic precipitator
C loudspeaker
D transformer [MJ2014/P12/Q34]

43 As a magnet is moved into the coil of wire as shown, there is a small reading on the sensitive
ammeter.

N S

Which change increases the size of the reading?

A moving the opposite pole into the coil

B pulling the magnet out of the coil
C pushing the magnet in faster
D unwinding some of the turns of wire [MJ2014/P12/Q36]
44 The diagram shows a 12 V d.c. power supply connected across a coil with a metal core.
The core becomes a magnet when the current is switched on. It remains a magnet after the
current is switched off.
metal core
From which metal is the core made?

A aluminium
12 V d.c.
B copper power supply coil of wire
C soft iron
D steel
[ON2014/P11/Q27]

45 The diagram shows a current-carrying wire in a horizontal magnetic field.

Which arrow shows the direction of the force experienced by the wire?

A
C magnetic
field

D [ON2014/P11/Q30]
current

46 The diagram shows a d.c. motor with its coil horizontal.

axle

N S

d.c. supply

Why is a split-ring commutator used?

A to change the current direction in the coil as the coil passes the horizontal position
B to change the current direction in the coil as the coil passes the vertical position
C to change the current direction in the d.c. supply as the coil passes the horizontal position
D to change the current direction in the d.c. supply as the coil passes the vertical position

[ON2014/P11/Q31]
47 Which graph shows the voltage output of an a.c. generator when the coil makes one complete
revolution?
A B

voltage voltage

0 0
0 time 0 time

C D

voltage voltage

0 0
0 time 0 time

[ON2014/P11/Q32]

48 Two long, parallel conductors carrying current lie in a horizontal plane.

The two conductors attract one another.

The two currents must

A be in the same direction.

B be in opposite directions.
C be parallel to the Earth’s magnetic field.

D be at 90° to the Earth’s magnetic field. [ON2014/P12/Q31]

49 The diagram shows a d.c. motor with its coil horizontal.
axle

N S

d.c. supply

Why is a split-ring commutator used?

A to change the current direction in the coil as the coil passes the horizontal position
B to change the current direction in the coil as the coil passes the vertical position
C to change the current direction in the d.c. supply as the coil passes the horizontal position
D to change the current direction in the d.c. supply as the coil passes the vertical position
[ON2014/P12/Q32]

50 A student moves a magnet into a coil of wire as shown in the diagram. The coil of wire is
connected to a sensitive ammeter.
coil

S N

magnet

ammeter

Which change does not produce an increase in the reading?

A increasing the number of turns on the coil

B increasing the resistance of the ammeter
C increasing the speed of the magnet
D increasing the strength of the magnet [ON2014/P12/Q33]
51 The coil of an a.c. generator is rotated and the output is displayed on the screen of a cathode-ray
oscilloscope (c.r.o.).

The diagram shows the trace on the screen.

Which trace appears on the screen when the speed of rotation of the coil is doubled but the
settings on the c.r.o. are unaltered?

A B C D

[ON2014/P12/Q34]

52 The diagram shows the magnetic field pattern of a current in a solenoid.

solenoid

K L M

When the current in the solenoid is increased, where is there an increase in the magnetic field
strength?

A K, L and M
B K and L only
C M and L only
[MJ2015/P11/Q27]
D M only
53 A magnet is placed near to a solenoid that is connected to a sensitive centre-zero ammeter.
solenoid

magnet

A
sensitive ammeter

The magnet is pushed towards the solenoid. It accelerates, then moves at constant speed, then
decelerates and stops inside the solenoid.

When is the reading on the ammeter zero?

A when the magnet is accelerating

B when the magnet is moving at constant speed
C when the magnet is decelerating
D when the magnet is stationary [MJ2015/P11/Q36]

32 P and Q represent two, parallel, straight wires carrying currents into the plane of the paper. P and
Q exert a force on each other.

Which arrow shows the force on Q?

Q
P D B

[ON2015/P11/Q32]
C
33 The diagram shows a simple d.c. motor.

What is the part labelled Q?

A a coil
B a commutator
C a magnet
D a slip ring [ON2015/P11/Q33]

35 Electric power cables transmit electrical energy over large distances using high-voltage,
alternating current.

What are the advantages of using a high voltage and of using an alternating current?

advantage of using a high voltage advantage of using an alternating current

A high current is produced in the cable the resistance of the cable is reduced
B high current is produced in the cable the voltage can be changed using a transformer
C less energy is wasted in the cable the resistance of the cable is reduced
D less energy is wasted in the cable the voltage can be changed using a transformer

[ON2015/P11/Q35]

31 The diagram shows the magnetic field around wire X which carries a current into the paper.

The arrows on the field lines show the direction of the force on

A a N-pole.
B a S-pole.
C a small negative charge.
D a small positive charge. [ON2015/P12/Q31]
32 P and Q represent two, parallel, straight wires carrying currents into the plane of the paper. P and
Q exert a force on each other.

Which arrow shows the force on Q?

Q
P D B

[ON2015/P12/Q32]
C

P 1 Mark Scheme
 P 2 Past Papers

01 (a) A wire carrying a current in a magnetic field experiences a force due to the current.
On Fig. 1.1, insert the words current, field and force in the boxes to show the relative
directions of the current, the magnetic field and the force.

Fig. 1.1
[3]

[MJ2011/P21/Q8]
02 Fig. 2.1 shows a rotating magnet in an alternating current generator that is used to power a lamp.

magnet

soft iron
N S

coil

lamp

Fig. 2.1

(a) (i) State how an alternating current differs from a direct current.

...........................................................................................................................................

...........................................................................................................................................

...................................................................................................................................... [1]

(ii) Explain, in detail, how alternating current is produced by the apparatus shown in
Fig. 2.1.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...................................................................................................................................... [4]

(iii) State two ways in which the current in the lamp may be increased.

1. ........................................................................................................................................

2. ........................................................................................................................................
[2]
(b) The generators at a power station produce a voltage of 25 000 V. This voltage is stepped up
to 400 000 V by a transformer for long-distance transmission on overhead power lines. The
voltage is later stepped down to 240 V.

(i) State and explain why the voltage is stepped up for long-distance transmission.

...........................................................................................................................................

...........................................................................................................................................

...................................................................................................................................... [2]

(ii) Calculate the ratio of the number of turns in the primary coil of the step-up transformer to
the number of turns in its secondary coil.

ratio = .......................................................... [1]

(iii) State one advantage and one disadvantage of using thicker wire in the overhead power
lines.

advantage: .........................................................................................................................

...........................................................................................................................................

disadvantage: ....................................................................................................................

...........................................................................................................................................
[2]

(iv) An electric drill of power 1000 W is used in a country where the mains voltage is 240 V.
State and explain the most appropriate fuse to use with this drill.
You should select a fuse from the following values: 1 A, 3 A, 4 A, 13 A.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...................................................................................................................................... [3]

[MJ2011/P21/Q9]
03 When a car is moving, its electrical equipment is powered by an a.c. generator.

(a) The coil of the a.c. generator is rotated by the car engine.

(i) On the axes in Fig. 3.1, sketch a graph of the output voltage of the coil against time for
two rotations of the coil of the generator.

output
voltage

0
0 time

[1]
Fig. 3.1

(ii) The speed of the car increases and so does the speed of rotation of the coil.

State two changes that this causes to the output voltage.

change 1 ............................................................................................................................

...........................................................................................................................................

change 2 ............................................................................................................................

...........................................................................................................................................
[2]

[ON2011/P21/Q6]
04 Fig. 4.1 shows part of an electric bell.

S
iron
bar

iron
core N

Fig. 4.1

A switch and a cell are in series with a length of wire coiled around an iron core.

The switch is closed and the current in the wire produces a south pole S and a north pole N at
the ends of the core, as shown in Fig. 4.1. Magnetic poles are also produced in a small iron bar,
placed near to the ends of the core.

(a) (i) On Fig. 4.1, mark with an N the position of the north pole produced in the iron bar and
mark with an S the position of the south pole produced in the iron bar. [1]

(ii) State and explain what happens to the iron bar once it is magnetised.

...........................................................................................................................................

.......................................................................................................................................[2]

(b) The switch is opened and there is no current in the wire. State what happens to the magnetic
poles in the iron bar.

...................................................................................................................................................

...............................................................................................................................................[1]

[ON2011/P22/Q5]
05 Fig. 5.1 shows two coils of insulated wire wound on an iron ring. Coil A is connected to a battery
and a switch. The switch is open. Coil B is connected to a sensitive centre-zero voltmeter.

coil A iron ring

open
switch

centre-zero
voltmeter

coil B

Fig. 5.1

The switch is closed. There is a current in coil A.

(a) On Fig. 5.1,

(i) mark the direction of the current in coil A, [1]

(ii) draw the magnetic field lines produced in the iron ring. [3]

(b) As the switch is closed, the voltmeter deflects to the right and then returns to zero.

(i) Explain why there is a deflection on the voltmeter.

...........................................................................................................................................

...........................................................................................................................................

.......................................................................................................................................[2]

(ii) The switch is opened. State and explain what happens to the deflection on the voltmeter.

...........................................................................................................................................

...........................................................................................................................................

.......................................................................................................................................[2]

(iii) Without changing coil A, state two changes to the apparatus that cause a greater
deflection of the voltmeter.

1. ........................................................................................................................................

2. ........................................................................................................................................
[2]
[MJ2012/P22/Q9]
06 (a) Fig. 6.1 shows a solenoid made from wire wound around a plastic cylinder.

plastic
cylinder

+ –

Fig. 6.1

A current in the solenoid produces a magnetic field.

On Fig. 6.1, draw the pattern of the magnetic field lines inside and outside the cylinder.
[2]

(b) Fig. 6.2 shows a beam of beta-particles, in a vacuum, passing into a magnetic field.

beta-particles magnetic field

out of the page

Fig. 6.2

The movement of the beta-particles from left to right is an electric current.

(i) On Fig. 6.2, draw an arrow to show the direction of the conventional current. [1]
(ii) A solenoid is used to produce the magnetic field that lies within the shaded region
of Fig. 6.2. The direction of the field is out of the page.

1. On Fig. 6.2, draw the path followed by one of the beta-particles in the shaded
region. [2]

2. The direction of the current in the solenoid is reversed. State what happens to
the path of the beta-particle.

...........................................................................................................................

...................................................................................................................... [1]

[ON2012/P21/Q7]
07 Fig. 7.1 shows a simple transformer.

core

alternating
current
supply

primary coil secondary coil

Fig. 7.1

(a) State the metal used for the core of a transformer.

...................................................................................................................................... [1]

(b) Explain how an alternating current in the primary coil causes the lamp to light.

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

...................................................................................................................................... [3]

(c) Transformers are used to produce high voltages for the transmission of electrical power
over long distances.

State one advantage of high voltage transmission.

..........................................................................................................................................

..........................................................................................................................................

...................................................................................................................................... [1]

[MJ2013/P21/Q8]
08 Fig. 8.1 shows a view, from above, of two wires X and Y. These wires carry equal currents
vertically downwards through a piece of card.

card

wire X
wire Y

A B

magnetic
field line

Fig. 8.1

One complete magnetic field line is drawn around each wire.

In this question, ignore the effects of the Earth’s magnetic field.

(a) On Fig. 8.1, draw the complete magnetic field line due to the current in wire X that
passes through point A.
Mark the direction of this field line. [2]

(b) Point B is midway between the two wires. Explain why the magnetic field at B is zero.

..........................................................................................................................................

..................................................................................................................................... [1]

(c) There is a force on wire Y due to the current in wire X.

(i) State the direction of the force on wire Y.

............................................................................................................................. [1]

(ii) Explain why there is a force on wire Y.

..................................................................................................................................

............................................................................................................................. [1]

[MJ2013/P22/Q7]
9 EITHER

Fig. 9.1 shows a simple a.c. generator. The coil is turning and an e.m.f. is induced in the coil.

Fig. 9.1

(a) The generator contains a permanent magnet. State the name of a metal used in a
permanent magnet.

..................................................................................................................................... [1]

(b) At the instant shown in Fig. 9.1, the induced e.m.f. is a maximum.

(i) Explain why the induced e.m.f. is a maximum.

..................................................................................................................................

..................................................................................................................................

..................................................................................................................................

............................................................................................................................. [2]

(ii) State the position of the coil where there is no induced e.m.f.

..................................................................................................................................

............................................................................................................................. [1]

[MJ2013/P22/Q8]
10 Fig. 10.1 shows a coil of wire connected by flexible leads to a switch and a battery.

Fig. 10.1

The coil is placed between the poles of a permanent magnet and is free to turn about the axis.

When the switch is closed, forces due to the current act on the sides of the coil. The coil starts to
turn.

(a) On Fig. 10.1, draw arrows to show the directions of the forces. [2]

(b) The coil stops when it is vertical. Explain why the turning effect of the forces is zero at this
position.

...................................................................................................................................................

.............................................................................................................................................. [1]

(c) In order for the coil to rotate continuously, a split-ring commutator is connected between the
battery and the coil.

Explain how the split-ring commutator enables the coil to rotate continuously. Include a
diagram in your answer.

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

.............................................................................................................................................. [4]

[MJ2014/P21/Q6]
11 A straight length of copper wire lies horizontally between the poles of a U-shaped magnet. Fig.
11.1 shows the two ends of the wire connected to a very sensitive, centre-zero ammeter.

copper wire

N S

sensitive, centre-zero ammeter

Fig. 11.1

The copper wire is moved upwards slowly between the two magnetic poles. The needle on the
ammeter deflects to the right.

(a) Explain why the needle on the ammeter deflects.

...................................................................................................................................................

...................................................................................................................................................

...............................................................................................................................................[2]

(b) The wire is moved downwards very quickly between the two magnetic poles.

State what happens to the needle on the ammeter.

...................................................................................................................................................

...............................................................................................................................................[1]

(c) State what happens to the needle on the ammeter when the copper wire is moved horizontally
between the two poles.

...................................................................................................................................................

...............................................................................................................................................[1]
[ON2014/P21/Q7]
12 Fig. 12.1 shows the structure of a simple alternating current (a.c.) generator.

output
terminals

Fig. 12.1

(a) On Fig. 12.1, label

• the coil of the generator with the letter C,

• a slip ring with the letter S,
• a carbon brush with the letter B.
[2]

(b) The a.c. generator is operating and the arrows on Fig. 12.1 show the direction of rotation.

Explain why there is an electromotive force (e.m.f.) between the two output terminals.

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...............................................................................................................................................[3]

[ON2014/P22/Q8]
13 A simple apparatus used to demonstrate electromagnetic induction is shown in Fig. 13.1.

support
spring

S
movement magnet
N

coil LED

Fig. 13.1

The coil is connected to two light-emitting diodes (LEDs). The magnet moves into and out of the
coil.

(a) Explain why there is an induced e.m.f. in the coil when the magnet moves.

...................................................................................................................................................

...................................................................................................................................................

...............................................................................................................................................[2]

(b) Explain why one LED lights up when the magnet moves into the coil and the other LED lights
up when the magnet moves out of the coil.

...................................................................................................................................................

...................................................................................................................................................

...............................................................................................................................................[2]

(c) The LEDs are brighter when the magnet moves faster.
Explain why.

...................................................................................................................................................

...................................................................................................................................................

...............................................................................................................................................[1]

[MJ2015/P21/Q7]
14 Fig. 14.1 shows a simple a.c. generator.

rotation
of coil
coil

N S

output voltage

Fig. 14.1

(a) The coil rotates and an alternating electromotive force (e.m.f.) is induced in the coil.

Fig. 14.2 shows how the alternating e.m.f. varies with time as the coil rotates.

+
e.m.f.

0
time

Fig. 14.2

Explain

(i) why an e.m.f. is induced,

...........................................................................................................................................

...........................................................................................................................................

...................................................................................................................................... [2]

(ii) why the e.m.f. is sometimes positive and sometimes negative.

...........................................................................................................................................

...........................................................................................................................................

...................................................................................................................................... [1]
(b) Changes are made to the a.c. generator, one at a time:

• stronger magnets are used

• more turns are wound on the coil
• the coil is turned faster.

Complete the table in Fig. 14.3 to show what happens to the maximum value of the e.m.f.
and to the frequency of the alternating e.m.f.

what happens to the maximum what happens to the frequency

changes made
value of the e.m.f. of the e.m.f.

stronger magnets

more turns on the coil

the coil is turned faster

Fig. 14.3
[3]

[MJ2015/P22/Q6]
15 (a) Fig. 15.1 shows a solenoid (long coil) X connected in series with a battery, a switch S and a
variable resistor (rheostat).

Fig. 15.1

The switch S is closed and there is a magnetic field due to the current in the solenoid.

(i) On Fig. 15.1, draw the pattern of the magnetic field in, above and below the solenoid.
[3]

(ii) A second solenoid Y is connected to a sensitive centre-zero ammeter. Solenoid Y is

placed in the magnetic field of X.

1. The resistance of the variable resistor is gradually decreased and the pointer of the
sensitive ammeter deflects slightly to one side.

Explain why this happens.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

................................................................................................................................ [3]
 2. The switch S is now opened.

Describe and explain what happens to the deflection on the ammeter as the switch is
opened.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

................................................................................................................................ [3]

(b) Fig. 15.2 shows a transformer that consists of two coils wound on an iron core. The transformer
is connected to an electricity transmission cable.

primary coil secondary coil

iron core

Fig. 15.2

(i) Explain the purpose of the iron core in the transformer.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...................................................................................................................................... [2]

[ON2015/P21/Q10]
16 Thin wire, covered in plastic insulation, is used to make a solenoid (long coil). The solenoid is
connected to a sensitive ammeter. Fig. 16.1 shows the N-pole of a steel magnet placed next to the
solenoid.

X Y
steel magnet

N
solenoid

Fig. 16.1

Point X and point Y are on the axis of the solenoid.

(a) (i) Explain why plastic is an electrical insulator.

...........................................................................................................................................

...........................................................................................................................................

...................................................................................................................................... [1]

(ii) Explain why the magnet is not made from

1. aluminium,

............................................................................................................................... [1]

2. iron.

............................................................................................................................... [1]

(b) In one experiment, the magnet in Fig. 16.1 is moved to the left and passes into the solenoid.
The N-pole of the magnet travels from Y to X at a constant speed. As it moves, the ammeter
shows a small current.

(i) Explain why there is a current in the solenoid when the magnet is moving.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...................................................................................................................................... [3]

[ON2015/P22/Q10]
 P 2 Mark Scheme

Page 4 Mark Scheme: Teachers’ version Syllabus Paper

GCE O LEVEL – May/June 2011 5054 21

8 (a) all three correct: force, field, current B1

Page 4 Mark Scheme: Teachers’ version Syllabus Paper

GCE O LEVEL – May/June 2011 5054 21
9 (a) (i) d.c. current flows in one direction or
a.c. current flows in one direction then the other B1

(ii)
mention of magnetic field/flux B1
(magnetic) field lines // flux cuts coil // flux changes in coil B1
induction of voltage/current B1
something relevant reverses (e.g. field/flux cuts in one direction then the
other // N pole approaches then leaves // N pole approaches and S pole
approaches)
and link to a.c. B1

(iii) two of: thicker wires; more turns of coil; stronger magnet; faster rotation;
lower resistance (of lamp) B2

(b) (i) to reduce heat/energy/power loss (on the power lines) B1

(higher voltage means) lower current B1

(ii) 25:400 // 1:16 // 0.0625 B1

(iii) reduces resistance // less power loss // costs less to run // more current //
more power B1
increases weight // more support needed // more wind resistance // more ice
forms // costs more to install B1

(iv) 13 A B1
(I =) P/V // 4.2 A // 4.17 etc A B1
must choose higher value to avoid fuse blowing // other fuses melt B1 [15]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper

GCE O LEVEL – October/November 2011 5054 21
6 (a) (i) recognisable sine/cosine curve (≥ 2.0 cycles) B1

(ii) larger (peak)(voltage) B1

higher frequency/shorter period/described in words (allow shorter
wavelength) B1

Page 3 Mark Scheme: Teachers’ version Syllabus Paper

GCE O LEVEL – October/November 2011 5054 22
5 (a) (i) N at top end of bar and S at bottom end B1

(ii) attracted to/moves towards iron core B1

unlike poles attract B1
(b) they disappear/bar is demagnetised/loses its poles/is weaker B1 [4]
 Page 5 Mark Scheme: Teachers’ version Syllabus Paper
GCE O LEVEL – May/June 2012 5054 22
9 (a) (i) conventional current direction correct in coil/one lead B1

(ii)
at least 1 line axially through coil A
OR line above and below end of coil A B1

at least two curved lines in ring from ends of A

to ends of B (and inside A and B) B1

correct direction on at least one line/arrow for candidate’s (i) B1

(b) (i) (magnetic) flux/field cuts (coil B)
OR field/flux changes (in coil B) B1

induces an e.m.f./voltage/current (in B) B1

(ii) (voltmeter) deflects to left/opposite (and returns to zero) B1

flux/field decreases/collapses/reduces
OR iron loses magnetism
OR change in field is in opposite direction
OR to oppose flux/field change B1

(iii) ANY 2 lines

more turns on coil B
larger voltage/current (e.g. of battery)/more cells
battery smaller (internal) resistance
smaller resistance of wires; thicker wires; shorter wires
thicker or shorter iron ring; use soft iron;
coil A and B closer (on ring);
more sensitive voltmeter; laminate the iron ring B2

Page 3 Mark Scheme Syllabus Paper

GCE O LEVEL – October/November 2012 5054 21

7 (a) (at least) two parallel horizontal lines within the cylinder B1
(at least) two correctly shaped lines outside the cylinder B1

(b) (i) (right to left) and on diagram (somewhere) B1

(ii) 1. path continuously curving in same direction M1

upwards (ignore lines outside the shaded area) A1
2. (changes to) downwards (curve) not reverses/opposite direction B1 [6]
 Page 3 Mark Scheme Syllabus Paper
GCE O LEVEL – May/June 2013 5054 21
8 (a) (soft) iron/mu-metal B1

(b) magnetic field or flux or flux/magnetic lines mentioned B1

changing magnetic field or changing flux or flux lines cut coil B1
induced voltage/current/e.m.f. B1

(c) less power/energy/heat loss (allow no power loss/to prevent power loss) or
more efficient or thinner wire can be used (ign. cheaper) B1 [5]

Page 4 Mark Scheme Syllabus Paper

GCE O LEVEL – May/June 2013 5054 22

7 (a) oval/circle through or near A centered on or near X B1

clockwise arrow on line(s) around X and none wrong B1

(b) fields (due to X and Y) cancel or X and Y fields equal and opposite B1

(c) (i) to the left

or towards X/A/B B1

(ii) current (in wire Y) and (magnetic) field (caused by other wire) B1 [5]
or two (magnetic) fields interact

Page 4 Mark Scheme Syllabus Paper

GCE O LEVEL – May/June 2013 5054 22
8 EITHER

(a) steel / magnadur / alnico / magnetite B1

(b) (i) mention of cutting (lines of) magnetic field / change in (magnetic) flux M1

great(est) rate of change A1

or fast(est) cutting
or other explanation involving time

(ii) vertical/upright B1
or turned through 90°
or normal to (magnetic) field
 Page 3 Mark Scheme Syllabus Paper
GCE O LEVEL – May/June 2014 5054 21
6 (a) arrows on long sides in opposite vertical directions [B1]
downwards on right and upwards on left or correct rotation shown [B1]

(b) no (horizontal) distance between forces or forces through axle / pivot / axis [B1]

(c) two halves of split ring clear and clearly connected to each end of coil [B1]
contacts / brushes labelled or described and connected to battery [B1]
each side of split ring touches other terminal / brush or current reverses in coil
or changes terminals of connection to battery [B1]
forces reverse on sides of coil or forces always in same direction on side
nearest a pole [B1]

[7]

Page 3 Mark Scheme Syllabus Paper

Cambridge O Level – October/November 2014 5054 21
7 (a) wire cuts field lines B1
current / e.m.f. / voltage induced B1

(b) larger deflection and to the left / opposite direction B1

(c) no deflection / current B1 [4]

Page 3 Mark Scheme Syllabus Paper

Cambridge O Level – October/November 2014 5054 22
8 (a) one label correct and not contradicted C1
C, 1S and 1B all correct and clear and none contradicted A1

(b) any three from:

magnetic field (between poles)
(coil / wire) cuts field / flux or field / flux cuts (coil / wire) or field / flux changes
(electromagnetic) induction
brushes rub against / in contact with rings B3

Page 3 Mark Scheme Syllabus Paper

Cambridge O Level – May/June 2015 5054 21

7 (a) field lines of magnet mentioned or magnetic flux mentioned B1

field lines cut the coil or flux changes B1

(b) reversed movement of magnet causes one of B1

• reversal of (induced) emf
• reversal of (induced) current
• field lines cut / flux change in reverse direction
LED emits light when current passes in one direction B1

(c) more current or more induced emf B1

and flux lines cut faster or faster change in flux
 Page 3 Mark Scheme Syllabus Paper
Cambridge O Level – May/June 2015 5054 22
6 (a) (i) mention of (magnetic) field / flux (of N and S-poles) C1
(coil/wire) cuts magnetic field / flux / lines A1
or magnetic flux in coil changes

(ii) (one side of) coil cuts one way and then the other B1
or (side) moves one way and then the other / returns
or flux increases and then decreases

(b) increase in emf for both stronger magnets and more turns B1
no change / same frequency for both stronger magnets and more turns B1
increase and increase for turn the coil faster B1

Page 4 Mark Scheme Syllabus Paper

Cambridge O Level – October/November 2015 5054 21

10 (a) (i) at least two straight parallel lines inside the coil B1
at least two (complete) lines one above the coil and one below the coil B1
third line in middle and evenly spaced and two closed loops B1
(any crossings max. 2 / 3)

(ii) current (in X) increases B1

magnetic field becomes stronger / changes B1
current / e.m.f. / voltage induced in Y / electromagnetic induction B1
opposite deflection B1
larger deflection B1
magnetic field decreasing or quicker (rate of) change B1 [9]

(b) (i) to increase the strength of the magnetic field B1

to direct / concentrate the magnetic field (into the secondary coil) B1

(ii) (P = )VI or 33 000 × 85 C1

2.8 × 106 W or 2800 kW or 2.8 MW A1

(iii) (E = )VIt or 33 000 × 85 × 3600 or 2.8 × 106 × 3600 C1

1.0 / 1.01 / 1.008 × 1010 J A1 [6]

Page 4 Mark Scheme Syllabus Paper

Cambridge O Level – October/November 2015 5054 22

10 (a) (i) no free electrons (in plastic) or all electrons are bound / structural B1
(ii) (aluminium) is not magnet(ic) or cannot be magnetised B1
(iron) is a temporary / soft magnetic material or is not a permanent magnet B1 [3]
(b) (i) magnetic field / flux (mentioned) B1
(magnetic) field lines cut wire / solenoid / circuit or changing magnetic
field / flux B1
voltage/e.m.f. induced B1
(ii) (V = )IR or 0.045 × 1.2 or 0.000045 × 1.2 C1
5.4 × 10–5 V or 0.054 mV A1
(Q = )It or 0.045 × 0.14 or 0.000045 × 0.14 C1
6.3 × 10–6 C or 0.0063 mC A1 [7]