KS3 Phx 8J EQ 60marks Magnets 4Students ... · Web viewThe simplified diagram shows a device which...

Name

KS3 Phx 8J EQ 60marks Magnets 4StudentsQ1. A pupil does four experiments with bar magnets and small, unmagnetised iron bars.She places

them as shown below. For each experiment, tick one box to show the effect of the magnetic force between the two objects.

4 marks

www.SmashingChemistry.com of 16

http://www.SmashingChemistry.com/

Q2. The diagram shows an electromagnetic relay. The relay is connected in a circuit with a battery, a lamp and a switch.

(a) (i) Give the name of a suitable material to use for the core of the electromagnet.

................................................................................................................................................. [1 mark] (ii) Give the name of a suitable material to use for the armature.

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

................................................................................................................................................. [1 mark] (b) (i) Explain why the contacts come together when the switch is closed.

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

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

................................................................................................................................................ [3 marks] (ii) When the switch is now opened, the bulb stays on. Explain why.

................................................................................................................................................. [1 mark]Q3. The diagram below shows three trolleys.Peter put a bar magnet on each trolley.

(a) He pushed trolleys A, B and C together.• Magnet B attracted magnet A.• Magnet B repelled magnet C.

On the diagram above, label the north and south poles of magnets A and C.Use the letters N and S.

2 marks

(b) Peter turned trolley B around. Trolleys A and C were not turned around.

What would happen now when Peter pushed them all together?Use either attract or repel to complete each sentence below.

Magnet B would .................................... magnet A. Magnet B would .................................... magnet C.

1 mark



(c) Peter held two trolleys close together and then let go.

The magnets repelled each other. Draw an arrow on both magnets to show which way they would move.

1 mark (d) Peter took a magnet, a steel bar and an aluminium bar. He put them on three trolleys as shown below.

(i) What happens to the steel bar as he moves it closer to the magnet?

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

(ii) What happens to the aluminium bar as he moves it closer to the magnet?

................................................................................................................................................. [1 mark]Q7. Mary used the apparatus below to test the strength of an electromagnet.She used the reading

on the newton meter to measure the force of the magnet on theiron disc.

(a) Explain why the reading on the newton meter increases when a current passesthrough the coil.

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



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

(b) When a current passes through the coil, some of the electrical energy is changedto thermal energy.What would happen to the coil if the current passing through it was too large?

................................................................................................................................................. [1 mark](c) Mary made two electromagnets, one with 100 turns of wire in the coil and onewith 200

turns.She varied the current through the coil of each electromagnet.She measured the force of each electromagnet on the iron disc.The graph shows her results.

Write two conclusions that Mary could make from these results.

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

2. ....................................................................................................................[2 marks]Q9. The diagram shows a magnetic lock for a door. It consists of both a strong permanent

magnet and an electromagnet. It is fitted into the door frame. An iron plate is attached to the door.

(a) In the diagram the switch is open. Explain why the door cannot be opened.

................................................................................................................................................. [1 mark] (b) When the switch is closed the door may be opened. Explain why the door may now be

opened.



................................................................................................................................................. [1 mark] (c) A burglar tries to get in by cutting the wires to the battery. Explain why the door still cannot

be opened.

................................................................................................................................................. [1 mark] (d) When the wires are repaired, the battery is accidentally connected the other way round. Explain why the door cannot now be opened.

................................................................................................................................................. [1 mark](e) Another magnetic lock is shown below. It does not have a permanent magnet in it.

Explain how this kind of lock works and why it is not as secure as the one shown at the beginning of the question.

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

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

Q10. The simplified diagram shows a device which protects people from being electrocuted when using power tools such as hedge cutters. The wire in one part of the circuit is shown darker to make the circuit clearer.When the armature is attracted towards the soft iron core, the contacts are pushed apart and break the circuit.

(a) The power tool, coil A and coil B are all in the same series circuit. Coils A and B are wound in opposite directions.The current in the coils has no magnetic effect on the armature. Explain why.

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



(b) A gardener accidentally cuts the wire at point X. Current from the power supply starts to flow through the gardener to earth.What effect will this have on the armature? Explain your answer.

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

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

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

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

................................................................................................................................................. [3 mark]Q11. Circuit breakers are switches which open when the current becomes too large. The diagram

shows a simple circuit breaker. The springy piece of metal pushes down on the iron rocker, and this holds the switch contacts together.

(a) (i) There is a current in the coil in the circuit breaker. What is the purpose of the coil?

................................................................................................................................................. [1 mark] (ii) What is the purpose of the soft iron core in the coil?

................................................................................................................................................. [1 mark] (b) Give two properties of iron which make it a good choice of material for the rocker.

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

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

(c) The diagram below shows the circuit breaker with the switch contacts open.

Why do the switch contacts separate when the current becomes too large?

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



Q12. The diagram shows a rectangular coil and circuit. It has two iron rods in it.The rods are parallel and touching. They are free to move.

(a) When the switch is closed, the two rods move apart.(i) Explain why this happens.

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

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

(ii) The switch is then opened to break the circuit. What, if anything, happens to the two iron rods?

................................................................................................................................................. [1 mark] (b) One of the two iron rods is taken out and replaced with a brass rod.The rods are parallel and

touching.What, if anything, will happen to the rods when the switch is closed?Explain your answer.

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

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

Q13. The diagram shows an electromagnet used in a door lock.

(a) The push switch is closed and the door unlocks. Explain in detail how this happens.

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

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

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



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



Q14. (a) The diagram below shows a car park barrier.

(i) Calculate the turning moment produced by the barrier about the pivot.Give the unit.

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

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

(ii) The barrier is horizontal. The weight of the barrier is balanced by an iron counterweight. Calculate the downward force produced by the counterweight.

................................................................................................................................................. [1 mark] (b) An electromagnet is placed beneath the iron counterweight as shown below.

When the switch is closed the barrier rises.Explain how the electromagnet can be used to raise the barrier.

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

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

Q15 A pupil fixes a small electromagnet close to a thin springy steel sheet. The device acts like a small

speaker. She connects a battery and switch to the electromagnet as shown.

(a) (i) When the pupil closes the switch, what will happen to the steel sheet?

................................................................................................................................................. [1 mark]www.SmashingChemistry.com of 16


(ii) The pupil opens the switch again. What will happen to the steel sheet now?

................................................................................................................................................. [1 mark] (iii) If the pupil had connected the battery the other way round, what difference would this

have made to your answer to part (i)?

................................................................................................................................................. [1 mark] (b) The pupil removes the battery and switch. She connects the electromagnet to a power

supply which switches the current on and off 1000 times each second. The steel sheet vibrates and makes a sound.

(i) She then adjusts the power supply so that the current is switched on and off 3000 times each second.

What difference does this make to the pitch of the sound?

Give a reason for your answer.

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

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

(ii) The pupil now adjusts the power supply so that the current is larger. Explain why this makes the sound louder.

................................................................................................................................................. [1 mark]Q16. David made two electromagnets as shown below.He used paper-clips to test the strength of

each electromagnet.He switched on the power supply in both circuits.

(a) How can you tell that the strength of both electromagnets is the same?

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



(b) David switched off the power supply in both circuits.The paper-clips fell off the iron core, but not off the steel core.

Why is iron used, rather than steel, for the core of an electromagnet?Use the diagrams above to help you.

................................................................................................................................................. [1 mark] (c) David used a sensor to measure the strength of an electromagnet. He placed the sensor 25 mm from the electromagnet and increased the current inthe coil. He repeated the experiment with the sensor 50 mm from the electromagnet. The graph below shows his results.

(i) How did the distance of the sensor from the electromagnet affect the reading on the sensor?

................................................................................................................................................. [1 mark] (ii) How did the size of the current in the coil affect the strength of the electromagnet?

................................................................................................................................................. [1 mark] (iii) What else could David do to an electromagnet to change its strength?

................................................................................................................................................. [1 mark]www.SmashingChemistry.com of 16


Mark Scheme M1. A no effect

1 (L3)B they attract

1 (L3)C they repel

1 (L4)D they attract

1 (L3)if more than one box is ticked

award no markM2. (a) (i) iron

1 (L6)(ii) iron or steel

1 (L6) (b) (i) any three from• current flows in the coildo not accept ‘the circuit is

completed’• the core becomes magnetisedaccept ‘the coil becomes an

electromagnet’ or ‘the electromagnet is turned on’

• the armature is attracted• the armature pushes the contacts togetherdo not accept ‘the contacts come

together’3 (L7)

(ii) the answer must show an understanding that the contactsremain closed

because current continues through the contactsor because the contacts keep the circuit complete

accept ‘the contacts are in parallel with the switch’or ‘the contacts stay shut’do not accept ‘there is a complete circuit’or ‘the current still flows’

1 (L7)M3. marks may be awarded for part

(a) if the magnets are correctly labelled in part (b) and no answer is given in part (a)

(a) • Magnet A

both poles are required for the mark

1 (L4)• Magnet C

both poles are required for the mark

1 (L4)

(b) • repel• attract

answers must be in the correct order

both answers are required for the mark

1 (L4)

(c) •

both arrows are required for the mark

1 (L4) (d) • it is attractedaccept ‘it gets faster’

1 (L4)• nothingaccept ‘it is not attracted or

repelled’accept ‘it is not attracted’ accept

‘it is not repelled’ ‘they stick together’ is insufficient

do not accept ‘it repels’1 (L4)

M7. (a) • the core becomes magnetised

accept ‘the disc becomes magnetised’accept ‘there is a magnetic field’accept ‘it becomes an (electro)magnet’accept ‘the stronger the current the stronger the magnet’

do not accept ‘the iron core becomes magnetic’

do not accept ‘the magnet gets stronger’

1 (L7) any one from• the core attracts the iron discaccept ‘the disc is pulled down’‘the disc moves down’ is

insufficient as it does not imply that a force is exerted

• there is more force on the iron discaccept ‘the magnet exerts a force

on the disc’‘there is a force on the disc’ is

insufficient as it does not refer to the origin of the force

1 (L7) (b) any one from• it would meltaccept ‘it would fuse’‘the coil would break’ is

insufficient



• it would get too hotaccept ‘it could catch fire’accept ‘it would

blow’‘it would get hot’ is insufficient

1 (L7) (c) • the greater the current, the greater

the force or fieldaccept the converseanswers must refer to a pattern

describinga continuous variabledo not accept ‘it becomes more magnetic’

• the more turns, the greater the force or field

accept the converseaccept ‘the more turns, the more

powerfulor stronger the magnet’

answers must include a comparison‘the more turns, the more powerful it is’ is insufficient

accept ‘the electromagnet with 200 turns is stronger’accept ‘doubling the turns more than doubles the force’

award one mark if the answer refers toa number of coils rather than number of turns

2 (L7)M9. (a) any one from• the permanent magnet attracts the iron

plateaccept ‘the magnet or magnetic

field holds it’• you cannot overcome the magnet accept ‘the permanent magnet is

still working’ or’ the magnet is too strong’

1 (b) the field of the electromagnet opposes

or cancels the field of the permanent magnet

accept ‘the electromagnet acts against the magnet’

do not accept ‘force holding door to plate is stopped’ or ‘electromagnet repels plate’ or ‘magnetic field is switched off’

1 (c) any one from• the permanent magnet still attracts the

iron plate or holds the dooraccept ‘the permanent magnet

will not be affected by this’• the electromagnet cannot cancel or

oppose the magnetic fieldaccept ‘the electromagnet cannot

be turned on’• the door cannot open unless there is a

current

accept ‘the door can only open when electricity or power is on’

1 (d) the field of the electromagnet

reinforces the field of the permanent magnet

accept ‘the electromagnet reinforces the magnet’or ‘the electromagnet also pulls the iron plate’

do not accept ‘poles now the wrong way round’or ‘poles are now the same way round’

1 (e) one mark is for the explanation that

current causes the electromagnetto work; the other mark is for the repercussions of a current failure

any one from• the electromagnet will hold the door shut

only when there is currentaccept ‘it only works when the

magnet is switched on’• if there is no current, the magnetic field

stops• it will be possible to open the door in a

power failureor by cutting the wire or if the battery is flat

do not accept ‘it is not as safe or secure’

M10. (a) any one from• the current flows in opposite directions so

there is no magnetic fielddo not accept ‘the currents in A

and B cancel outso there is no field’or ‘the coils are wound in opposite directions

• because the two magnetic fields or forces cancel out

do not accept ‘they cancel out’1

(b) there is no current in coil Aaccept ‘there is current in coil B

only’or ‘the currents in the coils are

different’or ‘coil A will lose its magnetic field’do not accept ‘there is current in coil B’

1 the magnetic fields no longer cancelaccept ‘the iron core becomes

magnetised’or ‘the magnetic fields are

different’1



the armature will be attracted or pulled towards the core

answers may be in any order1

M11. (a) (i) to produce a magnetic field or make an electromagnet

accept ‘to make the iron or core or it magnetic’ or ‘to make a magnet’

do not accept ‘to conduct the current’

1 (L7) (ii) any one from• to make the magnetic field stronger• to make the electromagnet strongeraccept ‘to focus or carry the field

lines’do not accept ‘to make an

electromagnet’or ‘to make the electromagnet better’

1 (L7) (b) it is magnetic

1 (L7) it conducts electricity

1 (L7)answers may be in either orderaccept ‘it is attracted to the coilor

core or electromagnet’accept ‘it conducts’ (c) any one from• the electromagnet overcomes the springy

metal• the moment of the electromagnet’s force

is biggerthan the moment of the spring’s force

accept ‘the pull of the electromagnet becomesmore than the pull of the spring

1 (L7)M12. (a) (i) any two from• the current in the coil produces a

magnetic fieldaccept ‘the current produces a

magnetic field’or ‘the coil produces a magnetic field’or ‘the coil becomes an electromagnet’

• the rods are magnetised in the same direction

accept ‘the N or S poles are next to each other’

• the rods repel each other2 (L7)

(ii) nothing or they stay where they areaccept ‘they become

demagnetised’1 (L7)

(b) nothing happens1 (L7)

because only the iron rod becomes

magnetised or because the brass roddoes not become magnetised

accept ‘because brass is not magnetic’

1 (L7)M14. (a) (i) 75accept ‘50 × 1.5’

1 (L7) Nmdo not accept lower case n

1 (L7)(ii) 750

accept ‘ ’ or ‘50 × 15’accept the numerical answer to

part (i) ÷ 0.11 (L7)

(b) any one from• a current flows in the coil• the coil or the iron core becomes

magnetisedaccept ‘there is a magnetic

field’or ‘the electromagnet switches on

do not accept ‘the core becomes magnetic’

1 (L7)any one from• the counterweight is attracted to the coil

or core or the electromagnet• the electromagnet produces a bigger

momentaccept ‘the left-hand side of the

barrier moves down’‘the right-hand side moves up’ is

insufficient1 (L7)

M15. (a) (i) any one from• attracted to the electromagnetaccept ‘attracted’ or ‘sticks to the

electromagnet’• bends towards the electromagnetaccept ‘moves left’ or ‘bends in’

or ‘bends’do not accept ‘vibrates’ or ‘makes a noise’or ‘becomes magnetised’ without qualification

1 (L7) (ii) any one From• goes back to where it wasaccept ‘ not attracted any more’or

returns to normal’• springs back• bends back• it straightensdo not accept ‘nothing’ or ‘it

stops vibrating’1 (L7)

(iii) any one from



• none or no difference• it would still attractdo not accept ‘bends the other

way’1 (L7)

(b) (i) higher pitchaccept ‘higher’ if both higher and

loudergiven award no mark1 (L7)

because the frequency of the vibration increases

accept ‘because the steel sheet vibratesfaster or moves faster’

do not accept ‘it vibrates more’1 (L7)

(ii) any one from• larger amplitude vibrationsaccept ‘bigger vibrations’ or

‘larger amplitude’or ‘more energy’do not accept ‘it vibrates more’• sheet would bend more or further

1 (L7)M16. (a) • both picked up the same

number or four paper-clipsaccept ‘they both picked up the

same number’accept ‘same amount of paper-

clips’accept ‘there were 5 out of 9

paper-clips left for both’accept ‘the same mass of paper-

clips’‘they hold the same clips’ is

insufficient1 (L5)

(b) any one from• it does not stay magnetised• it can be turned offaccept ‘you cannot turn steel off’• objects do not stay attached to it• iron loses its magnetism• steel stays magnetised

1 (L6) (c) (i) any one from• the greater the distance the lower the

reading• the further away the smaller the readingaccept the converse accept ‘at big distance the field is

weaker’ or the converseaccept ‘at 50 mm the reading is

lower’accept the conversedo not accept ‘the bigger the

distance the smaller the ampsor current’

1 (L6) (ii) • the greater the current the stronger

the electromagnet

1 (L6) (iii) any one from• change the number of turns• change the thickness of the wire• change the diameter of the coreaccept ‘use more coils’accept ‘use fewer or less coils’accept ‘put the coils closer

together’ or the converseaccept ‘change the metal of the

coils’accept ‘use a different sized core’accept ‘use nickel or cobalt core’accept ‘use a different core’‘use bigger coils’ is insufficient‘use more wire’ is insufficientdo not accept ‘add more

batteries’1 (L6)



KS3 Phx 8J EQ 60marks Magnets 4Students ... · Web viewThe simplified diagram shows a device which...

Documents

Transcript of KS3 Phx 8J EQ 60marks Magnets 4Students ... · Web viewThe simplified diagram shows a device which...