Mark scheme
■■6 Magnetism and electromagnetism
Practical work
Question
Answers and guidance
1
Answer identifies three faults for 1 mark each:
Not controlling variables (i.e. placing two magnets next to each other)
Not controlling variables (not using the same compass)
Not saying how to measure variables (e.g. distance between compass
and magnet)
Identifies one correction per fault for 1 mark each:
Use one magnet at a time; use the same compass each time; measure
how far the compass is from the magnet when the compass changes
direction
Total
3
3
6
Question
Answers and guidance
2 a)
Correct heading: number of cells or voltage (V)
Correct heading: distance (cm or m)
Space for four different voltage readings
1
1
1
b) i)
The electromagnet (and its position) must stay the same
1
Changing the electromagnet changes the strength of the magnetic
field it creates
1
ii)
Total
Marks
5
Question
Answers and guidance
3
Check the direction of the plotting compass needles with no magnet
Put the plotting compasses around the two magnets
Note the direction of the compass needles and draw field lines which
link them
Add arrows on the field lines in the direction from N to S
Total
Marks
1
1
1
1
4
Question
Answers and guidance
4 a)
The compasses show different parts of the field line at the same time
so the shape of the whole field line can be observed easily
OR
The plotting compasses can be moved
to look in detail at different parts of the field line
1
1
Arrange plotting compasses around the wire
Turn the current on and off
The compass needles line up with the Earth’s field when the current is
off/they line up with the electromagnet’s field when current is on
1
1
1
b)
Total
38
Marks
Marks
1
1
5
© Hodder & Stoughton 2013
6 Magnetism and electromagnetism
Question
Answers and guidance
5 a)
The wire between the magnets will move
It will move upwards
Reference to Fleming’s left hand rule (which links the direction of the
force, magnetic field and current)
1
1
1
b)
A larger resistance reduces the current
A smaller current reduces the electromagnetic force/the wire moves
less
(or the reverse argument)
1
1
c)
Same length
Same width/cross-sectional area
1
1
Total
Marks
7
Calculations
Question
Answers and guidance
1 a)
Vp/Vs = Np/Ns
230/Vs = 4000/100 = 40
Vs = 230/40 = 5.75 V ≈ 6 V
1
1
1
b)
VpIp = VsIs
230 × Ip = 5.75 × 0.9
Ip = 0.0225 A (or Ip = 0.0235 A if you use Vs = 6 V)
1
1
1
c)
Any two for 1 mark each:
The coils are heated by their currents
There can be magnetic field loss from the transformer core
Currents can be induced in the transformer core which generates heat
2
Total
Marks
8
Question
Answers and guidance
2 a) i)
Vs/Vp = Ns/Np
400 000/25 000 = Ns/10 000
Ns = 160 000
1
1
1
VpIp = VsIs
25 000 × 800 = 400 000 × Is
Is = 50 A
1
1
1
Any three points for 1 mark each:
When the secondary voltage is very high, the current carried by the
lines is lower
When the current is lower less power is wasted heating the lines
This saves energy and money
Also wires can be thinner
3
b)
ii)
Total
© Hodder & Stoughton 2013
Marks
9
39
Mark scheme
Question
Answers and guidance
Marks
3 a)
Vs/Vp = Ns/Np
Vs/230 = 5/500
Vs = 230 × 0.01 = 2.3 V
1
1
1
b)
I = V/R
= 2.3/0.02
= 115 A
1
1
c)
The wires are very thick so that their resistance is low
OR
The thick wires will not heat up
1
d)
P = VI
= 2.3 × 115
= 265 W
1
e)
P = VI
265 = 230 × I
I = 265/230
= 1.15 A
f)
g)
1
1
1
P = E/t
265 = 15 000/t
t = 15 000/265
= 57 s
1
1
1
Heat is conducted from the ends of the wire by the thick connecting
wires so the nail is hottest in the middle
Total
Question
1
14
Answers and guidance
4 a)
Marks
4.0
(b)
3.0
load/N
(a)
2.0
1.0
0
0
0.5
1.0
1.5
current/A
2.0
Points plotted accurately
Axes labelled
Line of best fit drawn
b)
Total
40
See the graph in part a)
The graph reaches the same maximum value
The maximum is reached for a lower current
(with more turns of wire the magnetic effect of the current increases,
so the magnet ‘saturates’ sooner)
2
1
1
1
1
6
© Hodder & Stoughton 2013
6 Magnetism and electromagnetism
Diagrams
Question
Answers and guidance
Marks
1 a) i)
X
ii)
b) i)
ii)
N
S
X
Correct shape
Number of lines (not crossing)
Direction N → S
Two Xs as on diagram
1
1
1
1
The field lines are closest together near the poles
Draw more field lines from the poles
1
1
Total
6
Question
Answers and guidance
2 a) i)
The field is of equal strength and in the same direction everywhere
Marks
1
ii)
N
S
Lines equally spaced
Lines in the same direction
Lines N → S
1
1
1
Circular lines
Arrows on lines in clockwise direction
The direction of the lines/magnetic field is in the other direction
(anticlockwise)
1
1
1
b) i)
ii)
c)
N
S
Three of the following points for 1 mark each:
A clockwise circular field close to the wire
Lines going N → S from the magnet
Lines going round the top of the wire, in the ‘catapult’ shape
Field stronger above than below
d)
B
S
A
C
N
D
The coil turns clockwise (through a quarter of a full revolution)
Total
© Hodder & Stoughton 2013
3
2
1
13
41
Mark scheme
Question
Answers and guidance
3 a) i)
The magnet induces a voltage when it moves inside the coil
The voltage changes direction, when the magnet changes direction –
it moves up and down
1
1
b) i)
The magnet is moving at its greatest speed
(this happens when it is in the middle of its movement – up or down)
The magnet is not moving
This is because it has reached the end of an oscillation
1, 1
ii)
c)
Two of the following for 1 mark each:
Use a stronger magnet
Use more turns of wire
Use a stiffer spring, so the magnet moves faster
Use a less massive magnet, so it moves faster
(No mark for saying ‘use a more sensitive data logger’– the data
logger is not part of the seismometer)
Total
Marks
1
1
2
8
Question
4 a)
Answers and guidance
thumb
Marks
first finger
second
finger
i)
ii)
b)
Use this rule: thuMb – Motion
First – magnetic Field
seCond – Current
The rod moves to the right
The left-hand rule shows that there is a force on the bottom of the
disc into the plain of the paper, which makes the disc rotate
The disc rotates clockwise
AB the force is down
CD the force is up
The coil rotates anticlockwise
Total
1
1
1
1
6
Question
Answers and guidance
5 a) i)
Any two points for 1 mark each from:
Move the trolley to the right
Reverse the magnetic field
Move the magnet to the left
Switch the connections A and B around
Move the trolley faster
Use stronger magnets
zero
2
When the frame swings through the magnetic field, kinetic energy is
transferred to electrical energy
This does not happen in A, so the frame stops more quickly in B
1
ii)
iii)
b)
Total
42
1
1
Marks
1
1
1
1
7
© Hodder & Stoughton 2013
6 Magnetism and electromagnetism
Question
Answers and guidance
Marks
6 a)
(i)
(ii)
b)
Voltage half the peak voltage
Time period twice as long
(The marks are awarded for a smaller voltage and longer time period)
1
1
For a voltage to be induced the magnet must be moving in the coil
When the bicycle is stationary the coil is stationary so no current flows
in the coil or lamp
1
1
Total
4
Longer-answer questions
Question
Answers and guidance
1
An alternating current flows in the coil of wire
The current-carrying wire coil and magnet are attracted/repelled
As the current changes direction, the direction of the electromagnetic
force changes direction
The coil/cone vibrates/moves in and out
The cone produces a sound wave
Total
Marks
1
1
1
1
1
5
Question
Answers and guidance
2
When the switch closes, the current flows
The electromagnet becomes magnetic/is magnetised
and it attracts the soft iron bar
which pulls the clapper to the bell/makes a sound
This breaks the circuit
so the clapper/iron bar returns to starting position which completes
the circuit again
Total
Marks
1
1
1
1
1
1
6
Question
Answers and guidance
3
Step-up transformers increase the voltage from the power station
power = voltage × current
High voltage in power lines reduces the current
Low currents cause less heating in the wires
Less energy is transferred to the surroundings as heat/more energy is
transmitted as electricity
The step-down transformers reduces the voltage to safe levels
Total
© Hodder & Stoughton 2013
Marks
1
1
1
1
1
1
6
43
Mark scheme
Question
Answers and guidance
4
An a.c. voltage (current) is supplied to the primary coil
The alternating voltage creates an alternating magnetic field in the iron
core
This magnetic field in the core induces an alternating voltage (current)
in the secondary coil
There are fewer turns in the secondary coil than the primary coil/It is a
step-down transformer
The turns rule says the ratio of turns equals the ratio of voltage in
each coil/Having fewer turns in the secondary coil reduces the output
voltage (current)
Total
Marks
1
1
1
1
1
5
Question
Answers and guidance
5
Lightweight so it does not create more work for the cyclist
Good contact with tyre so it can spin as the wheel turns
Strong magnet to induce a large voltage
Many turns on the coil to induce a large voltage
Total
Marks
1
1
1
1
4
Question
Answers and guidance
Marks
6
Identifies two ways to increase the power, for 1 mark each:
By using more batteries
By using more turns of wire
By using stronger magnets
2
Lists three advantages and/or disadvantages for one of these
methods, for 1 mark each:
Some batteries are very compact
Using two batteries instead of one doubles the power output
Narrow wire is needed to make a lot of turns on the coil/it can be hard
to make tightly wound turns on a coil
If the coil has lots of turns, lots more turns are needed to double
the power by much/adding more turns has little effect on the power
output
Increasing the turns on the coil has little effect on its size
3
1
Explain the choice (1 mark):
Add extra batteries but choose compact ones so the power doubles
but the weight doesn’t increase too much
OR
Add extra turns to the coil but use very narrow wire and coil it very
tightly to save space
OR
Use the strongest magnet possible
Total
44
6
© Hodder & Stoughton 2013