Oxford Revise AQA GCSE Physics | Chapter P17 answers

P17: Magnets and electromagnets

Answers

Extra information

Mark

AO / Specification reference

01.1

from AB to CD/ABCD

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AO2

4.7.2.2

4.7.2.3

01.2

the forces are the same size

but in opposite directions/side AB goes up, side CD goes down

so the coil spins clockwise

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1

1

AO2

4.7.2.3

01.3

the current in BC is parallel to the magnetic field

Fleming’s Left Hand rule says that the current must be perpendicular to the field for a force to act

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1

AO2

4.7.2.2

4.7.2.3

01.4

the coil has momentum

so continues to move until the coil is in contact with the battery again on the other side

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1

AO2

4.7.2.3

4.5.7.1

02.1

the Earth’s magnetic field

systematic error

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1

AO2

4.7.1.2

02.2

subtract the measurements in 2.1 from each of the readings

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AO3

4.7.1.2

02.3

the sensor cannot be zero cm from the wire as that would be the centre of the wire/inside the wire

1

AO2

4.7.2.1

02.4

If quantities are inversely proportional, then doubling one quantity will halve the other

when the distance doubles from 1cm to 2cm the magnetic field goes from 0.203 mT for 0.102 mT

\(\frac{0.102}{0.203} = 0.5\)

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1

1

AO1

AO2

4.7.2.1

03.1

a permanent magnet is always magnetic

an induced magnet becomes magnetic when it is put in a magnetic field but then loses its magnetism when it is removed from the field

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1

AO1

4.7.1.1

03.2

yes

(it has become an induced magnet) any magnet has a magnetic field around it

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1

AO1

AO2

4.7.1.1

03.3

left box (closest to screwdriver) ‘S’, right box ‘N’

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AO2

4.7.1.1

03.4

no

it is no longer magnetic when it is removed from the magnetic field

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1

AO2

4.7.1.1

04.1

independent: material of the core

dependent: mass of iron filings

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1

AO2

4.7.2.1

04.2

number of turns of the solenoid/coil

current in the wire

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1

AO2

4.7.2.1

04.3

nickel allow second measurement/1.0 g for nickel alloy

they did not include it

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1

AO3

4.7.2.1

04.4

small

if there was lots of nickel in the alloy, the mass of iron filings that it picks up would be large

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1

AO3

4.7.1.2

04.5

the core and armature should be made of iron

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AO2

04.6

when the switch is closed the coil of wire becomes an electromagnet

one end of the iron armature is attracted to the coil, causing it to rock on its pivot so that the other end of the armature

closes the contacts of the second switch in the high voltage circuit

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1

1

AO3

4.7.2.1

05.1

the wire will get hot when it is connected to the battery

only connect the wire for short periods of time

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1

AO2

AO3

4.7.2.1

05.2

magnetic field with the same shape as that of a bar magnet

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AO1

4.7.2.1

05.3

solenoid B

it has more turns/coils

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1

AO2/1

4.7.2.1

05.4

the compass needle does not move

as all the field lines are pointing in the same direction and the compass follows the direction of the field lines

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1

AO2

4.7.2.1

06.1

use a magnet/put a magnet near the coil

causing a force on the wire/a motor is a coil of current-carrying wire in a magnetic field

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1

AO2

4.7.2.3

06

Level 3: Correct identification of similarities and differences. Correct application of ideas about direct current/alternating current. Answer shows clear organisation.

5-6

AO1

AO2

AO3

4.7.2.3

4.7.2.4

Level 2: Some details of action of motor/loudspeaker missing. Answer shows some organisation.

3-4

Level 1: One or two similarities/difference given. No application of direct current to loudspeaker. Answer shows poor organisation.

1-2

No relevant content.

0

Indicative content:

  • both the motor and loudspeaker contain a coil of wire and a magnet
  • a simple d.c. motor contains a battery/source of direct current, but a loudspeaker uses a source of alternating current
  • both use the motor effect, but the force is in the same direction in the motor, but changes direction in the loudspeaker.
  • the loudspeaker coil would move out and stay there
  • no sound would be produced.

07.1

a region where a magnetic material experiences a force/a region around a magnet where magnetic forces act.

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AO1

4.7.1.2

07.2

one mark for arrows on lines pointing away from poles

one mark for shape of field

2

AO1

4.7.1.2

07.3

the magnetic field lines are close together

do not accept ‘there are more magnetic field lines’

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AO1

4.7.1.2

07.4

halfway between A and B

the force exerted by each magnet is the same

closer to A

the force on the object depends on the distance from the poles

the force by A is smaller, so the object needs to be closer

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1

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1

AO3

4.7.1.2

08.1

\(
\begin{array}{lr}
\rm{speed} = \frac{\rm{distance}}{\rm{time}}\\
3 \times 10^8 = \frac{{{\rm{distance}}}}{{{0}{\rm{.2}}}}\\
\rm{distance\ travelled\ by\ radio\ waves} = 3 \times 10^8 \times 0.2\\
= 6 \times 10^7\ \rm{m}\\
\rm{distance\ to\ asteroid} = \frac{6 \times 10^7}{0.2} = 3 \times 10^7\ \rm{m}
\end{array}
\)

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1

1 + 1

AO2

4.5.6.1.2

08.2

the range of values within which the true values lies

or words to that effect

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AO1

08.3

measure the distance to the object after a certain time interval

find the difference in distance

divide by the time between the pulses

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1

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AO3

4.5.6.1.2

09.1

the motor effect/there is a force on a current carrying conductor in a magnetic field

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AO2

4.7.2.2

09.2

the field around a magnet gets weaker as you move away

the field is not strong enough to produce a force

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1

AO2

4.7.1.2

09.3

place the magnetic field sensor a distance from the foil and measure the distance and magnetic field strength

move the sensor, measure distance and magnetic field strength again

make repeat measurements of the field at all the distances

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1

1

AO1

4.7.2.1

09.4

a graph showing a negative relationship

the graph shows that as distance increases magnetic field strength decreases

accept straight or curved line with negative gradient.

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1

AO2

4.7.2.2

10.1

(towards) north/the north magnetic pole of the Earth

there is a magnetic field around the Earth

further possible explanation: there is a gigantic south pole at magnetic north so the compass arrow head which is a N pole is attracted to the gigantic S pole at magnetic north

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1

AO1

AO2

4.7.1.2

10.2

the magnetic field around the wire is stronger than the magnetic field of the Earth

the needle of the compass changed direction when the current was switched on

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1

AO1

AO2

4.7.1.2

10.3

a compass needle is a magnet

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AO1

4.7.1.2

11.1

geographic north is the point about which the Earth spins

magnetic north is the point to which a compass points

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1

AO1

4.7.1.2

11.2

he used a compass

to look at the direction in which the compass points as he moved it around the model Earth

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1

AO3

4.7.1.2

11.3

new evidence/data

show that old models are incorrect and need to change

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1

AO2

4.7.1.2

11.4

so that other scientists can see/check/use their work/peer review

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AO1

4.7.1.2

12.1

one mark for half pints plotted correctly

one mark for all points plotted correctly

one mark for line of best fit

3

AO2

AO3

4.7.2.3

12.2

as the current increases the speed increases

at an increasing rate/rate is not constant/speed is not proportional to current

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1

AO3

4.7.2.3

12.3

force = magnetic field strength × current × length

force = mass × acceleration

as the current increases the force increases

as the force increases the acceleration increases

acceleration is the rate of change of speed/velocity

so the rate of change of speed/velocity increases

accept F = BIL

accept F = ma

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1

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1

AO1

AO3

4.5.6.2.2

4.7.2.2

4.7.2.3

13.1

to the right

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AO2/1

4.7.2.2

13.2

force = magnetic field strength × current × length

2 × 10–3 = magnetic field strength × 1.2 × 0.10

\(
\begin{array}{lr}
\rm{magnetic\ field\ strength\ B} = \frac{2 \times 10^{-3}}{1.2 \times 0.10}\\
= 0.017
\end{array}
\)

T/tesla

accept F = BIL

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1

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1

AO1

AO2

4.7.2.2

13.3

the magnetic field of the horseshoe magnet is uniform (straight lines between the poles) and going up/from N to S

the magnetic field of the rod is circular/concentric circles

when the fields are superimposed on top of each other, on one side of the rod all the field lines are in the same direction creating a strong field

on the other side some field lines cancel as in opposite directions so there is a weak field

the force makes the rod move from strong to weak field

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1

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AO1

AO3

4.7.1.2

4.7.2.1

4.7.2.2

14.1

ultraviolet light has a range of wavelengths/there is a band of frequencies that we call ultraviolet light

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AO1

4.6.2.1

14.2

red light has a lower frequency

red light has a longer wavelength

accept converse

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1

AO1

AO2

4.6.2.1

14.3

increases the risk of (skin) cancer

or

causes premature aging

accept DNA damage/mutation

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AO1

4.6.2.3

14.4

correct use:

  • tanning
  • checking for forgeries
  • killing insects
  • marking property which can be traced after burglary

accept correct alternative suggestions

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AO1

4.6.2.4

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