1. 1
   A recycling centre worker tests two unlabelled metal rods to sort scrap metal. She holds each rod near a magnetised electromagnet crane hook (switched on) so it becomes magnetised, then switches the electromagnet off and moves each rod away. Rod P remains strongly magnetic afterwards, able to pick up small steel paperclips on its own. Rod Q loses almost all of its magnetism straight away and can no longer pick up the paperclips.

   (a)

   What type of magnet is rod P behaving as?

   [1 mark]

   • AA permanent magnet, since it keeps its magnetism after the magnetising field is removed
   • BA temporary magnet, since it needs a constant current to stay magnetic
   • CAn induced magnet, since its magnetism appears only in the presence of another magnet
   • DA non-magnetic material, since it can pick up paperclips

   (b)

   What type of magnet is rod Q behaving as?

   [1 mark]

   • AA permanent magnet, since it was magnetised at all
   • BAn induced magnet, since it only stays magnetised while in a magnetic field and loses its magnetism once removed
   • CA non-magnetic material, since paperclips are attracted to it briefly
   • DAn electromagnet, since it needs an electric current

   (c)

   Steel and soft iron are both magnetic materials, but rod P is most likely made from steel and rod Q from soft iron. Explain, based on the results described, why this material difference explains the different behaviour of rods P and Q.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An electrician runs a long, straight underground cable horizontally beneath a garden to supply power to a shed. When a large direct current flows through the cable, a gardener notices that a small plotting compass placed on the ground directly above the cable deflects away from pointing north.

   (a)

   Why does the plotting compass deflect when current flows through the buried cable?

   [1 mark]

   • AThe cable heats the ground, which affects the compass needle's magnetism
   • BThe cable's insulation becomes magnetic when carrying current
   • CThe current in the cable creates its own magnetic field, which combines with the Earth's field to alter the direction the compass needle points
   • DThe compass detects the electric field around the cable directly

   (b)

   The gardener switches off the current, waits, and switches it back on again in the opposite direction. What would you expect to happen to the compass needle's deflection?

   [1 mark]

   • AIt stays deflected in exactly the same direction as before
   • BIt stops deflecting altogether, since reversing current cancels the magnetic field
   • CIt spins continuously, since reversing current makes the field spin
   • DIt deflects in the opposite direction, since reversing the current reverses the direction of the magnetic field it produces

   (c)

   State how the strength of the magnetic field produced around the cable depends on the size of the current and the distance from the cable.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student uses a small plotting compass to investigate the magnetic field around a single bar magnet placed on a sheet of paper. She places the compass at several points around the magnet and marks the direction the compass needle points at each position, then moves the compass a small distance in that direction, repeating from different starting points to build up whole field lines.

   (a)

   State the rule for the direction a plotting compass needle points at any location in a magnetic field, and state where the magnetic field around the bar magnet is strongest.

   [3 marks]

   (b)

   Explain how the student's method, of following the direction the compass points and marking a series of points, can be used to build up a picture of the magnetic field lines around the whole magnet, and explain how she could tell from her results where the field is weaker.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A scrapyard crane uses an electromagnet made from a coil of insulated wire wound many times around a soft iron core, connected to a large direct current supply, to lift and drop pieces of scrap steel. Separately, the crane's conveyor belt is driven by a small electric motor containing a rectangular coil that carries a current while positioned between the poles of a permanent magnet.

   (a)

   Explain why using a soft iron core, rather than a steel core, is the better choice for the crane's electromagnet, and explain two ways the operator could increase the strength of the electromagnet's magnetic field without changing the core.

   [6 marks]

   (b)

   Inside the conveyor belt's motor, the current-carrying coil experiences a force because it is in the magnetic field of the permanent magnet. Explain, using the motor effect, how this force is produced on the current-carrying coil, and explain how the design of the motor ensures the coil keeps rotating continuously in one direction rather than stopping after a quarter turn.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A sailor notices that the compass on a small boat gives a slightly wrong reading whenever a magnetic loudspeaker, mounted in the cabin, is placed too close to it. When she moves the loudspeaker further away, the compass reads correctly again, pointing towards the Earth's magnetic north.

   (a)

   Why does the nearby loudspeaker's magnet disturb the compass reading?

   [1 mark]

   • AThe loudspeaker magnet's own magnetic field combines with the Earth's magnetic field near the compass, so the needle no longer points purely towards magnetic north
   • BLoudspeakers produce an electric field which the compass mistakes for a magnetic field
   • CThe compass needle becomes permanently demagnetised near any magnet
   • DSound waves from the loudspeaker physically push the compass needle

   (b)

   Once far enough away, the compass correctly points towards the Earth's magnetic north pole. What does the behaviour of a compass needle suggest about the Earth itself?

   [1 mark]

   • AThe Earth has no magnetic field of its own; compasses only respond to nearby metal objects
   • BThe Earth behaves as if it has a giant bar magnet inside it, producing a magnetic field that the compass needle aligns with
   • CThe Earth's magnetic field is created entirely by satellites orbiting overhead
   • DThe compass needle points towards the Sun rather than the Earth

   (c)

   State what this evidence, from a simple compass, suggests about the core of the Earth.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A security door uses an electromagnetic lock: a coil of wire (a solenoid) wound around a hollow tube, with a movable steel bolt inside. When current flows through the solenoid, the magnetic field it produces pulls the steel bolt into the tube, retracting the lock and allowing the door to open.

   (a)

   Which statement correctly describes the magnetic field inside the solenoid when current flows through it?

   [1 mark]

   • AThe fields from the individual coils cancel out inside the solenoid, leaving no field
   • BThe field is strongest just outside the solenoid and zero inside it
   • CThe fields from the individual coils add together to form a strong, almost uniform field along the centre of the solenoid
   • DThe field only exists at the two ends of the solenoid, with nothing in between

   (b)

   If the security team wants to make the electromagnetic lock pull with a stronger force without changing the coil, what could they do?

   [1 mark]

   • ADecrease the current flowing through the solenoid
   • BWind the same wire more loosely around the tube
   • CDisconnect alternating turns of the coil
   • DIncrease the current flowing through the solenoid

   (c)

   State two ways, other than changing the current, that the strength of the solenoid's magnetic field could be increased.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A straight copper wire, 0.6 m long, is placed at right angles to a uniform magnetic field of flux density 0.25 T. A current of 4 A flows through the wire.

   (a)

   Calculate the force exerted on the wire due to the magnetic field.

   [3 marks]

   (b)

   Explain how you would use Fleming's left-hand rule to find the direction of the force on the wire, and explain what would happen to the direction of the force if the current in the wire were reversed.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   An engineering student builds a small demonstration motor using a rectangular coil placed between the two poles of a horseshoe-shaped permanent magnet, so that the sides of the coil sit in the strong, uniform magnetic field in the gap between the poles. She first tests a version of the coil with a single loop of wire, then rewinds it with five loops of wire carrying the same current, keeping everything else the same.

   (a)

   Explain why a horseshoe magnet is a good choice for this motor, referring to the shape and strength of its magnetic field between the poles, and explain why the motor's coil is placed to sit inside the gap between the two poles rather than outside the magnet.

   [6 marks]

   (b)

   Explain, using the motor effect, why rewinding the coil with five loops instead of one, while keeping the current the same, increases the turning force on the coil, and explain one other change (other than the number of turns) that could further increase this turning force.

   [6 marks]

   Total for question 8: 12 marks

End of questions