Download KS3 Phx 8J EQ 60marks Magnets 4Students

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KS3 Phx 8J EQ 60marks Magnets 4Students
Q1.
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
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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.
.................................................................................................................................................
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................................................................................................................................................ [3 marks]
(ii) When the switch is now opened, the bulb stays on. Explain why.
Q3.
................................................................................................................................................. [1 mark]
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
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(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)
Q7.
What happens to the aluminium bar as he moves it closer to the magnet?
................................................................................................................................................. [1 mark]
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.
.................................................................................................................................................
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................................................................................................................................................. [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.
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................................................................................................................................................. [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]
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(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]
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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.
.................................................................................................................................................
Q13.
................................................................................................................................................. [2 mark]
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]
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Q14.
(a)
(i)
The diagram below shows a car park barrier.
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]
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(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]
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Page 9 of 14
(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]
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Mark Scheme
M1.
A
no effect
1 (L3)
B
they attract
C
they repel
order
both answers are required for the
mark
1 (L3)
1 (L4)
D
1 (L4)
(c)
•
they attract
1 (L3)
if more than one box is ticked
award no mark
M2.
(a) (i)
iron
1 (L6)
(ii)
iron or steel
1 (L6)
(b) (i)
any three from
• current flows in the coil
do not accept ‘the circuit is
completed’
• the core becomes magnetised
accept ‘the coil becomes an
electromagnet’ or ‘the
electromagnet is turned on’
• the armature is attracted
• the armature pushes the contacts together
do 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.
(a)
marks may be awarded for part
(a) if the magnets are correctly
labelled in part (b) and no answer is
given in part (a)
• Magnet A
both poles are required for the
mark
1 (L4)
•
Magnet C
both arrows are required for the
mark
1 (L4)
(d) • it is attracted
accept ‘it gets faster’
1 (L4)
• nothing
accept ‘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)
(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’
M7.
1 (L7)
any one from
• the core attracts the iron disc
accept ‘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 disc
accept ‘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)
both poles are required for the
mark
1 (L4)
(b) • repel
• attract
answers must be in the correct
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(b) any one from
• it would melt
accept ‘it would fuse’
‘the coil would break’ is
insufficient
• it would get too hot
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accept ‘it could catch fire’accept ‘it would
blow’
‘it would get hot’ is insufficient
1 (L7)
• the greater the current, the greater
the force or field
accept the converse
answers 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 converse
accept ‘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
(c)
2 (L7)
M9.
(a) any one from
• the permanent magnet attracts the iron
plate
accept ‘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 door
accept ‘the permanent magnet
will not be affected by this’
• the electromagnet cannot cancel or
oppose the magnetic field
accept ‘the electromagnet cannot
be turned on’
• the door cannot open unless there is a
current
accept ‘the door can only open
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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 current
accept ‘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 field
do 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 A
accept ‘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 cancel
accept ‘the iron core becomes
magnetised’
or ‘the magnetic fields are
different’
1
the armature will be attracted or pulled
towards the core
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answers may be in any order
1
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 stronger
accept ‘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 order
accept ‘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 field
accept ‘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 other
2 (L7)
(ii) nothing or they stay where they are
accept ‘they become
demagnetised’
1 (L7)
(b)
nothing happens
1 (L7)
because only the iron rod becomes
magnetised or because the brass
roddoes not become magnetised
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accept ‘because brass is not
magnetic’
1 (L7)
M14.
(a) (i)
accept ‘50 × 1.5’
75
1 (L7)
Nm
do not accept lower case n
1 (L7)
(ii)
750
accept ‘
’ or ‘50 × 15’
accept the numerical answer to
part (i) ÷ 0.1
1 (L7)
(b) any one from
• a current flows in the coil
• the coil or the iron core becomes
magnetised
accept ‘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
moment
accept ‘the left-hand side of the
barrier moves down’
‘the right-hand side moves up’ is
insufficient
1 (L7)
M15.
(a) (i)
any one from
• attracted to the electromagnet
accept ‘attracted’ or ‘sticks to the
electromagnet’
• bends towards the electromagnet
accept ‘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 was
accept ‘ not attracted any more’or
returns to normal’
• springs back
• bends back
• it straightens
do not accept ‘nothing’ or ‘it stops
vibrating’
1 (L7)
(iii) any one from
• none or no difference
• it would still attract
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do not accept ‘bends the other
way’
1 (L7)
(b) (i)
higher pitch
accept ‘higher’ if both higher and
loudergiven award no mark
1 (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 vibrations
accept ‘bigger vibrations’ or
‘larger amplitude’
or ‘more energy’
do not accept ‘it vibrates more’
• sheet would bend more or further
• change the number of turns
• change the thickness of the wire
• change the diameter of the core
accept ‘use more coils’
accept ‘use fewer or less coils’
accept ‘put the coils closer
together’ or the converse
accept ‘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 insufficient
do not accept ‘add more
batteries’
1 (L6)
1 (L7)
(a) • both picked up the same
number or four paper-clips
accept ‘they both picked up the
same number’
accept ‘same amount of paperclips’
accept ‘there were 5 out of 9
paper-clips left for both’
accept ‘the same mass of paperclips’
‘they hold the same clips’ is
insufficient
M16.
1 (L5)
(b) any one from
• it does not stay magnetised
• it can be turned off
accept ‘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 reading
accept the converse
accept ‘at big distance the field is
weaker’ or the converse
accept ‘at 50 mm the reading is
lower’
accept the converse
do 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
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