Motors and transformers
P3
62 minutes
62 marks
Page 1 of 27
Q1.
A student has made a simple electric motor. The diagram shows the electric motor.
(a)
Complete the following sentence by drawing a ring around the correct line in the box.
the cell
Once the coil is spinning, one side of the coil is pushed by
the coil
and the other
a force
side is pulled, so the coil continues to spin.
(1)
(b)
Suggest two changes to the electric motor, each one of which would make the coil spin
faster.
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2 .....................................................................................................................
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(2)
(c)
Suggest two changes to the electric motor, each one of which would make the coil spin in
the opposite direction.
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2 ........................................................................................................................
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(2)
(Total 5 marks)
Page 2 of 27
Q2.
(a) A science technician sets up the apparatus shown below to demonstrate the motor
effect. He uses a powerful permanent magnet.
The copper roller is placed across the metal rails. When the switch is closed, the copper
roller moves to the right.
(i)
Complete the sentence by drawing a ring around the correct line in the box.
an electrical conductor.
This happens because copper is
an electrical insulator.
a magnetic material.
(1)
(ii)
Suggest one change that the technician can make which will cause the copper roller
to move faster.
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(1)
(iii)
Suggest two changes which the technician can make, each of which will separately
cause the copper roller to move to the left.
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2 ............................................................................................................
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(2)
Page 3 of 27
(b)
Many electrical appliances, such as vacuum cleaners, drills and CD players, contain
electric motors. As more electrical appliances are developed, more electricity needs to be
generated. Generating electricity often produces pollutant gases.
(i)
Complete the sentence by drawing a ring around the correct line in the box.
Generating more electricity to power the increasing number of electrical appliances
used
an ethical
raises
an environmental
issue.
a political
(1)
(ii)
The number of electrical appliances used in the world’s richest countries is
increasing yet many people in the world’s poorest countries have no access to
electricity.
What type of issue does this inequality between people in different countries raise?
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(1)
(Total 6 marks)
Q3.
(a)
Name a material that could be used to make the outside case of the plug.
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Give a reason for your choice.
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(2)
Page 4 of 27
(b)
To gain full marks in this question you should write your ideas in good English. Put them
into a sensible order and use the correct scientific words.
Some electrical circuits are protected by a circuit breaker. These switch the circuit off if a
fault causes a larger than normal current to flow. The diagram shows one type of circuit
breaker. A normal current (15 A) is flowing.
Source: adapted from V. PRUDEN and K. HIRST, AQA GCSE Sceince
Reproduced by permission of Hodder and Soughton Educational Ltd
Explain what happens when a current larger than 15A flows. The answer has been started
for you.
When the current goes above 15 A, the electromagnet becomes stronger and
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(3)
(Total 5 marks)
Page 5 of 27
Q4.
The diagram shows the equipment used by a student to investigate the strength of five
different electromagnets.
The stronger the electromagnet, the more paper clips it will hold.
(a)
Why is it important that the paper clips used in the investigation are all the same size?
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(1)
(b)
The five electromagnets, J, K, L, M and N, used by the student are shown below.
Each electromagnet was made by wrapping lengths of insulated wire around identical iron
nails.
The student wants to find out how the strength of an electromagnet depends on the
number of turns of wire in the coil.
Which electromagnets should the student compare in order to do this?
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(1)
Page 6 of 27
(c)
The student concluded:
“The strength of an electromagnet is always directly proportional to the number of turns on
the coil.”
(i)
Explain how the data from the investigation supports the student’s conclusion.
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(2)
(ii)
The student makes one more electromagnet by winding 100 turns onto a nail.
Before testing the electromagnet, the student predicted the number of paper clips
that the electromagnet would hold when the current is 1 amp.
How many paper clips should the student predict that the electromagnet would hold?
Show clearly how you work out your answer.
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number of paper clips = .....................................
(2)
(iii)
When the student tested the electromagnet it held 20 paper clips.
This is not what the student predicted.
Explain what the student should do when new data does not seem to support the
prediction that was made.
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(3)
(Total 9 marks)
Page 7 of 27
Q5.
Batteries inside laptop computers are charged using laptop chargers. The laptop charger
contains a traditional transformer.
(a)
The alternating current flowing through the primary coil of the transformer creates an
alternating current in the secondary coil.
Explain how.
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(3)
Page 8 of 27
(b)
(i)
Use information from the diagram to calculate the potential difference the charger
supplies to the laptop.
Use the correct equation from the Physics Equations Sheet.
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Potential difference = .......................................................... V
(2)
(ii)
Calculate the current in the primary coil of the transformer when the laptop is being
charged.
Assume the transformer is 100% efficient.
Use the correct equation from the Physics Equations Sheet.
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Current = .......................................................... A
(2)
Page 9 of 27
(c)
Switch mode transformers can be used in mobile phone chargers.
Switch mode transformers and traditional transformers can both use the UK mains supply.
The switch mode transformer is smaller and lighter than the traditional transformer used in
the laptop charger.
Give one other advantage of the switch mode transformer.
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(1)
(d)
Laptop batteries and mobile phone batteries can only be recharged a limited number of
times. After this, the batteries cannot store enough charge to be useful. Scientists are
developing new batteries that can be recharged many more times than existing batteries.
Suggest one other advantage of developing these new batteries.
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(1)
(Total 9 marks)
Page 10 of 27
Q6.
The diagram shows a device called a current balance.
(a)
(i)
When the switch is closed, the part of the wire labelled XY moves upwards.
Explain why.
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(2)
(ii)
What is the name of the effect that causes the wire XY to move?
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(1)
(iii)
An alternating current (a.c.) is a current which reverses direction. How many times
the current reverses direction in one second depends on the frequency of the
alternating supply.
Describe the effect on the wire XY if the battery is replaced by an a.c. supply having
a frequency of 5 hertz.
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(2)
Page 11 of 27
(b)
The diagram shows how a small weight can be used to make the wire XY balance
horizontally.
Use the data in the diagram and the equation in the box to calculate the force, F, acting on
the wire XY.
moment
=
force
×
perpendicular distance from the line of
action of the force to the axis of rotation
Show clearly how you work out your answer.
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Force = ............................................................ N
(3)
(Total 8 marks)
Page 12 of 27
Q7.
(a)
Some people wear magnetic bracelets to relieve pain.
Figure 1 shows a magnetic bracelet.
There are magnetic poles at both A and B.
Part of the magnetic field pattern between A and B is shown.
Figure 1
What is the pole at A? ...........................................
What is the pole at B? ...........................................
(1)
(b)
Figure 2 shows two of the lines of the magnetic field pattern of a current-carrying wire.
Figure 2
The direction of the current is reversed.
What happens to the direction of the lines in the magnetic field pattern?
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(1)
Page 13 of 27
(c)
Fleming’s left-hand rule can be used to identify the direction of a force acting on a currentcarrying wire in a magnetic field.
(i)
Complete the labels in Figure 3.
Figure 3
(2)
(ii)
Figure 4 shows:
•
the direction of the magnetic field between a pair of magnets
•
the direction of the current in a wire in the magnetic field.
Figure 4
In which direction does the force on the wire act?
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(1)
(iii)
Suggest three changes that would decrease the force acting on the wire.
1 ..........................................................................................................
2 ..........................................................................................................
3 ..........................................................................................................
(3)
Page 14 of 27
(d)
Figure 5 shows part of a moving-coil ammeter as drawn by a student.
The ammeter consists of a coil placed in a uniform magnetic field.
When there is a current in the coil, the force acting on the coil causes the coil to rotate and
the pointer moves across the scale.
Figure 5
(i)
The equipment has not been set up correctly.
What change would make it work?
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(1)
(ii)
Figure 6 shows the pointer in an ammeter when there is no current.
Figure 6
What type of error does the ammeter have?
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(1)
(Total 10 marks)
Page 15 of 27
Q8.
The diagram shows a transformer with a 50 Hz (a.c.) supply connected to 10 turns of
insulated wire wrapped around one side of the iron core.
A voltmeter is connected to 5 turns wrapped around the other side of the iron core.
(a)
What type of transformer is shown in the diagram?
Draw a ring around the correct answer.
step-down
step-up
switch mode
(1)
(b)
The table shows values for the potential difference (p.d.) of the supply and the voltmeter
reading.
p.d. of the supply
in volts
Voltmeter reading
in volts
6.4
3.2
3.2
6.4
(i)
Complete the table.
(2)
(ii)
Transformers are used as part of the National Grid.
How are the values of p.d. in the table different to the values produced by the National
Grid?
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(1)
Page 16 of 27
(c)
Transformers will work with an alternating current (a.c.) supply but will not work with a
direct current (d.c.) supply.
(i)
Describe the difference between a.c. and d.c.
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(2)
(ii)
Explain how a transformer works.
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(4)
(Total 10 marks)
Page 17 of 27
M1.
(a)
a force
1
(b)
any two from:
•
more powerful magnet
do not allow ‘bigger magnet’
•
reduce the gap (between magnet and coil)
•
increase the area of the coil
•
more powerful cell
do not allow ‘bigger cell’
accept battery for cell
accept add a cell
accept increase current / potential difference
•
more turns (on the coil)
allow ‘more coils on the coil’
do not allow ‘bigger coil’
2
(c)
reverse the (polarity) of the cell
allow ‘turn the cell the other way round’
accept battery for cell
1
reverse the (polarity) of the magnet
allow ‘turn the magnet the other way up’
1
[5]
M2.
(a)
(i)
an electrical conductor
1
(ii)
increase current
accept increase p.d. / voltage
or
use stronger magnets
accept move magnets closer
do not accept use larger magnets
1
(iii)
reverse the poles / ends (of the magnet)
either order
1
reverse the connections (to the power supply)
1
(b)
(i)
environmental
1
Page 18 of 27
(ii)
ethical
allow political (instability)
allow economic (migration)
1
[6]
M3.
(a)
plastic or rubber
accept any named plastic
do not accept wood
1
it is a (good) insulator or it is a poor conductor
ignore mention of heat if in conjunction with electricity
1
(b)
The answer to this question requires ideas in good English in a
sensible order with correct use of scientific terms. Quality of written
communication should be considered in crediting points in the mark scheme.
Maximum of 2 marks if ideas not well expressed.
pulls iron bolt down or attracts the iron bolt or moves bolt out of plunger
answers in terms of charges attracting
or repelling gain no credit
1
plunger pushed / moved to the right (by spring) or plunger released
1
push switch opens / goes to off / goes to right
accept circuit is broken
for maximum credit the points must follow a logical sequence
3 correct points but incorrect sequence scores 2 marks only
ignore reset action
1
[5]
M4.
(a)
so the results can be compared fairly
fair test is insufficient
1
(b)
JLM
all 3 required and no other
1
Page 19 of 27
(c)
(i)
for a given current the number of paper clips increases
by the same factor as the number of turns
1
plus a mathematical explanation using the data
eg a current of 1 A with 10 turns picks up 3 clips, a
current of 1 A with 20 turns picks up 6 clips
1
(ii)
30
allow 1 mark for showing correct use of figures eg
20 turns × 5 = 100 turns
2
(iii)
check the new data / repeat the experiment
1
to identify any anomalous results
1
then reconsider prediction / hypothesis in the
light of new evidence
1
[9]
M5.
(a)
(the alternating current creates) a changing / alternating magnetic field
1
(magnetic field) in the (iron) core
accept that links with the secondary coil
current in the core negates this mark
1
(causing a) potential difference (to be) induced in / across secondary coil
accept voltage for p.d.
1
(b)
(i)
20
allow 1 mark for correct substitution, ie
or
2
Page 20 of 27
(ii)
0.3
or
correct calculation using 230 × Ip = their (b)(i) × 3.45
allow 1 mark for correct substitution, ie
230 × Ip = 20 × 3.45
allow ecf from (b)(i) for 20
OR
substitution into this equation
2
(c)
(switch mode transformers) use (very) little power / current / energy when switched
on but no load is applied
accept no for little
ignore it is more portable
do not accept electricity for power / current / energy
or
it is more efficient
accept does not get as hot or less heat produced
1
(d)
any one from:
•
fewer (waste) batteries have to be sent to / buried in land-fill
•
the soil is polluted less by batteries in land-fill
•
fewer (waste) batteries have to be recycled
•
fewer batteries have to be made
•
less raw materials are used in making batteries
•
customers have to replace their batteries less often
longer lifetime is insufficient
•
customers have to buy fewer (replacement) batteries
it costs less is insufficient
1
[9]
M6.
(a)
(i)
current produces a magnetic field (around XY)
accept current (in XY) is perpendicular to the (permanent)
magnetic field
1
(creating) a force (acting) on XY / wire / upwards
reference to Fleming's left hand rule is insufficient
1
(ii)
motor (effect)
1
Page 21 of 27
(iii)
vibrate / move up and down
1
5 times a second
only scores if first mark point scores
allow for 1 mark only an answer ‘changes direction 5 times a
second’
1
(b)
0.005
allow 1 mark for calculating moment of the weight as 0.04 (Ncm)
and
allow 1 mark for correctly stating principle of moments
or
allow 2 marks for correct substitution
ie F × 8 = 2 × 0.02 or F × 8 = 0.04
3
[8]
M7.
(a)
north (pole)
accept N
north (pole)
both needed for mark
1
(b)
reverses
accept changes direction
1
(c)
(i)
first finger:
(direction of) (magnetic) field
1
second finger:
(direction of) (conventional) current
1
(ii)
into (plane of the) paper
1
(iii)
less current in wire
accept less current / voltage / more resistance / thinner wire
1
weaker field
allow weaker magnets / magnets further apart
do not accept smaller magnets
1
rotation of magnets (so) field is no longer perpendicular to wire
1
Page 22 of 27
(d)
(i)
reverse one of the magnets
do not accept there are no numbers on the scale
1
(ii)
systematic or zero error
accept all current values will be too big
accept it does not return to zero
accept it does not start at zero
1
[10]
M8.
(a)
step-down
1
(b)
(i)
1.6
correct order only
1
12.8
1
(ii)
values of p.d. are smaller than 230 V
1
(c)
(i)
a.c. is constantly changing direction
accept a.c. flows in two / both directions
accept a.c. changes direction(s)
a.c. travels in different directions is insufficient
1
d.c. flows in one direction only
1
(ii)
an alternating current / p.d. in the primary creates a changing / alternating
magnetic field
1
(magnetic field) in the (iron) core
current in the core negates this mark
accept voltage for p.d.
1
(and so) an alternating p.d.
1
(p.d.) is induced across secondary coil
1
[10]
Page 23 of 27
E1.
Nearly three quarters of students answered part(a) correctly. In (b)&(c), although better
answered than in previous series, students continue to have difficulties describing accurately
what changes need to be made to a motor to cause different effects. Some still only state what
needs to be changed without specifying in what way it is changed, in many of the answers the
descriptions were too vague to merit a mark.
E2.
(a)
(b)
E3.
(i) Although over half of candidates knew that the experiment worked because
copper is an electrical conductor, just under half of candidates thought it was
because copper is a magnetic material.
(ii)
Nearly three quarters of candidates were able to describe an acceptable way to
increase the speed of the copper roller. However in this question and the next many
candidates suggested tilting the rails to achieve the desired effect.
(iii)
Candidates lost marks in this question by not explaining clearly enough what they
meant, for example several mentioned moving the battery to the other side without
mentioning reversing the current or the connections and there were many incorrect
answers relating to the switch. However, more than two fifths of candidates gained at
least one mark. The most common correct answer related to reversing the magnetic
field in some way.
(i)
This was well answered with nearly all candidates gaining the mark.
(ii)
This was well answered with nearly two thirds of candidates giving the correct type of
issue.
Foundation Tier
The responses in part (a) was mostly worthy of credit.
(b)
There were abundant clues in both the stem of the question and the labels on the diagram
to start candidates on the correct sequence. However, rather too many candidates started
their answers with the iron bolt moving upwards with the result that they were unable to
logically explain the working of the circuit breaker.
Higher Tier
This question was particularly well answered by most candidates.
(a)
Most candidates gained both marks in this part but some gave heat insulation and failed to
mention electrical insulation.
(b)
There were some excellent answers to this part but a minority of candidates were unable
to explain how this type of circuit breaker works.
Page 24 of 27
E5.
(a) A poorly answered question, with almost half the candidates failing to gain any marks.
Candidates often failed to state that the magnetic field was changing, or failed to use the
word ‘induced’.
(b)
(i)
Most candidates scored both marks. Working was usually clear. Many of the
candidates struggled to re-arrange the equation.
(ii)
Half of the candidates scored 2 marks. Some candidates gained marks with an error
carried forward from their answer to (b)(i).
(c)
About one third of the students gained the mark.
(d)
Another question testing the societal aspects of scientific evidence. Half of the candidates
gained the mark. Many incorrect responses merely repeated information supplied in the
question.
E6.
(a)
(b)
E7.
(i)
Students rarely included the idea of the current producing a magnetic field around
the wire XY. Some students were clearly confused with the induction process.
(ii)
Just over half of students scored this mark.
(iii)
Just over half of students scored at least one mark. Incorrect responses included:
back and forth; spinning; faster; repelled instead of ‘up and down’. The frequency of 5
hertz was sometimes interpreted as once every five seconds.
There was a clear distinction in this question between the students who could do the
calculation perfectly and those who struggled. Some answers were left as fractions by
students without calculators; there were a number of 1 mark responses for calculating the
left hand moment. A number of students did not gain marks because of inconsistent units
and moving between cm and m.
(a) Just over half of the students knew that a magnetic field of repulsion between two poles
with lines of force moving outward from the poles was that between two north poles.
(b)
Nearly all students knew that reversing the current through a wire also reversed the
direction of the field lines associated with it.
(c)
(i)
Three-quarters of students knew which directions the first two fingers represent in
Fleming’s left-hand rule.
(ii)
Students were given a diagram of a wire carrying a current in a magnetic field. Using
Fleming’s left-hand rule the wire would move into the paper. Many students were
able to use the rule successfully, but their answers were ambiguous, such as
‘downwards’ and ‘away from you’. Less than a fifth of students scored the mark.
Page 25 of 27
(d)
E8.
(iii)
Over three quarters of the students knew that decreasing the current and the
strength of the magnetic field would decrease the force acting on the wire. Only a
tenth of the students knew that rotating the magnets so that the field was no longer
perpendicular to the wire would also have the same effect.
(i)
Most students observed that two south poles facing each other would not give a
uniform magnetic field and suggested that one of the magnets should be rotated.
(ii)
Less than three quarters of students knew that an ammeter pointing to a value above
zero when no current was in it, had a systematic or zero error.
(a) Most students recognised the transformer illustrated as being a step-down
transformer.
(b)
(c)
(i)
Most students were able to complete a table with values of potential difference from
the input and output of the transformer.
(ii)
Most students knew that the values of potential difference produced by the National
Grid were larger than those given in the question.
(i)
Only half of the students gave an adequate description of the difference between a.c
and d.c., for example, ‘a.c. flows in two directions whereas d.c. only flows in one
direction’. A quarter of students scored zero. Their explanations often used ‘ways’
instead of ‘directions’ and referred to ‘positive’ and ‘negative’.
(ii)
The explanation of how a transformer works was poorly answered with more than a
third of students scoring zero out of four.
Many answers only referred to the number of turns on each coil. Very few students
mentioned the changing magnetic field in the primary coil and others stated that
there was a current in the core.
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