1. 1
   A camper uses a torch powered by two AA cells and also plugs a portable fan into a mains socket at a campsite hook-up point.

   (a)

   Which statement correctly distinguishes the current supplied by the cells from the current supplied by the mains socket?

   [1 mark]

   • AThe cells supply direct current, which always flows in the same direction, whereas the mains socket supplies alternating current, which repeatedly changes direction
   • BThe cells supply alternating current, whereas the mains socket supplies direct current
   • CBoth the cells and the mains socket supply exactly the same type of current
   • DThe cells supply no current at all until connected to the mains

   (b)

   The campsite's mains supply has a frequency of 50 Hz. Which statement correctly describes what this frequency means for the current supplied to the fan?

   [1 mark]

   • AThe current changes direction only once every 50 seconds
   • BThe current completes 50 full cycles of direction change every second
   • CThe current flows in the same direction for 50 minutes before reversing
   • DThe frequency of 50 Hz refers to the voltage of the cells, not the mains supply

   (c)

   An oscilloscope trace of the torch's cell supply shows a constant, unchanging horizontal line, while a trace of the campsite mains supply shows a repeating wave pattern that rises above and falls below the time axis. Explain what each of these traces tells you about the type of current being supplied in each case.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An electrician installs a new washing machine in a kitchen. The washing machine has a metal outer casing that is connected to the earth wire of the mains supply, in addition to being protected by a fuse in its plug.

   (a)

   Which statement correctly explains the purpose of the earth wire?

   [1 mark]

   • AThe earth wire is only needed to connect the washing machine to the neutral wire
   • BThe earth wire increases the current delivered to the washing machine's motor to make it spin faster
   • CThe earth wire prevents the washing machine from using any electricity at all
   • DIf a fault causes the live wire to touch the metal casing, the earth wire provides a low-resistance path for a large current to flow, which blows the fuse and disconnects the appliance

   (b)

   The electrician explains that a circuit breaker could be used instead of a fuse to protect the washing machine circuit. Which statement correctly describes an advantage of a circuit breaker over a fuse?

   [1 mark]

   • AA circuit breaker never needs to disconnect a circuit, even during a serious fault
   • BA circuit breaker allows a fault current to keep flowing indefinitely, unlike a fuse
   • CA circuit breaker disconnects the circuit more quickly than a fuse and can be reset, rather than needing to be replaced
   • DA circuit breaker is a type of earth wire, not a switching device

   (c)

   Explain what happens inside a fuse when an excessive current flows through the washing machine's circuit due to a fault, and explain why this response protects the user from an electric shock.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A hairdryer has a plastic outer casing, rather than a metal one, and its instructions state that it does not require an earth wire.

   (a)

   Explain why a plastic-cased appliance can safely be sold without an earth connection, and identify the safety feature this design relies on.

   [3 marks]

   (b)

   The hairdryer still has a fuse fitted inside its plug even though it does not need an earth wire. Explain why a fuse is still necessary for a double-insulated appliance, referring to the kind of fault a fuse protects against that double insulation alone cannot prevent.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A landlord is renovating an old house and must decide whether to fit modern circuit breakers or traditional rewireable fuses to protect the electrical circuits in each room, as well as ensuring every metal-cased appliance socket is properly earthed.

   (a)

   Explain, comparing fuses and circuit breakers, which protective device the landlord should choose for the household circuits, and explain how earthing works alongside this device to protect anyone using an appliance with a metal casing.

   [6 marks]

   (b)

   During the renovation, a tenant later plugs a metal-cased toaster with a damaged internal wire into a socket that is properly earthed and protected by a correctly rated fuse. Explain, step by step, what happens electrically from the moment the live wire touches the metal casing to the moment the appliance is made safe, and evaluate why omitting either the earth wire or the fuse from this safety system would leave the tenant at risk.

   [6 marks]

   Total for question 4: 12 marks

End of questions