1. 1
   A hiker uses a plotting compass to find north while walking through a remote valley with no landmarks.

   (a)

   Which statement correctly explains why the compass needle always points towards the Earth's magnetic north pole?

   [1 mark]

   • AThe compass needle is a small magnet that aligns itself with the Earth's own magnetic field
   • BThe compass needle becomes electrically charged and is attracted to the north pole
   • CThe compass needle spins freely and always settles by chance in a north–south direction
   • DThe compass needle is repelled by gravity towards magnetic north

   (b)

   The hiker notices that whenever she brings the compass close to her steel walking pole, the needle is strongly attracted to the pole, even though the pole itself was not originally a magnet. Which term describes this effect?

   [1 mark]

   • AInduced magnetism
   • BElectromagnetic induction of current
   • CRadioactive decay
   • DRefraction

   (c)

   Explain, in terms of induced magnetism, why the steel walking pole attracts the compass needle when the compass is brought close to it, and explain what would happen to this attraction if the compass were moved far away from the pole.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An engineer designs a scrapyard crane that uses an electromagnet to lift and sort pieces of scrap steel. The electromagnet consists of a coil of insulated wire wound around a soft iron core, connected to a direct current supply.

   (a)

   Which change would increase the strength of the electromagnet's magnetic field?

   [1 mark]

   • AReducing the number of turns of wire in the coil
   • BRemoving the soft iron core from inside the coil
   • CIncreasing the current flowing through the coil
   • DSwitching the supply from direct current to no current at all

   (b)

   The operator wants to release the scrap steel that has been picked up by the electromagnet. Which of the following is the simplest way to do this?

   [1 mark]

   • AIncrease the current flowing through the coil
   • BReverse the direction of the current in the coil
   • CAdd more turns to the coil
   • DSwitch off the current flowing through the coil

   (c)

   Explain why an electromagnet, rather than a permanent magnet, is used in this scrapyard crane, referring to the ability to control the magnetic field.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A technician sets up a demonstration in which a straight, current-carrying wire is passed vertically through a horizontal sheet of card, with iron filings scattered on the card and a current flowing through the wire.

   (a)

   Describe the pattern of the magnetic field that the iron filings would form around the wire, and explain how the pattern would change if the current in the wire were increased.

   [3 marks]

   (b)

   The technician then winds the same wire into a solenoid (a long coil) and passes the same current through it. Explain why winding the wire into a solenoid produces a stronger and more useful magnetic field than the straight wire, and describe how the field pattern inside the solenoid differs from that around the straight wire.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An engineer is designing a new type of automated recycling sorter that uses an electromagnet on the end of a robotic arm to lift steel cans from a mixed pile of waste, while leaving aluminium cans and plastic behind.

   (a)

   Explain, using ideas about magnetic fields, magnetic materials and induced magnetism, how the electromagnet is able to selectively pick up only the steel cans, and explain how the design of the electromagnet (number of turns, current, and use of a core) could be altered to lift a larger number of cans at once.

   [6 marks]

   (b)

   The engineer decides to test the sorter by reversing the direction of the current supplied to the electromagnet's coil while it is holding a load of steel cans over a collection bin. Explain, using ideas about magnetic poles and induced magnetism, what would happen to the electromagnet's magnetic field and to the steel cans as a result, and explain why the electromagnet could not be used in the same way to sort permanently magnetised steel objects from aluminium ones.

   [6 marks]

   Total for question 4: 12 marks

End of questions