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P2.4.1 - AQA GCSE Physics Unit 2

 

 

P2.4.1

Household electricity

a) Cells and batteries supply current that always passes in the same direction. This is called direct current (d.c.).

See AC/DC

Candidates should be able to compare and calculate potential differences of d.c. supplies and the peak potential differences of a.c. supplies from diagrams of oscilloscope traces.

Higher Tier candidates should be able to determine the period and hence the frequency of a supply from diagrams of oscilloscope traces.

 

b) An alternating current (a.c.) is one that is constantly changing direction.

c) Mains electricity is an a.c. supply. In the UK it has a frequency of 50 cycles per second (50 hertz) and is about 230 V.

d) Most electrical appliances are connected to the mains using cable and a three-pin plug.

e) The structure of electrical cable.

 Candidates should be familiar with both two-core and three-core cable.
 

f) The structure and wiring of a three-pin plug.

 Knowledge and understanding of the materials used in three-pin plugs is required, as is the colour coding of the covering of the three wires.
 

g) If an electrical fault causes too great a current, the circuit is disconnected by a fuse or a circuit breaker in the live wire.

  
 

h) When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit.

  
 

i) Some circuits are protected by Residual Current Circuit Breakers (RCCBs).

Candidates should realise that RCCBs operate by detecting a difference in the current between the live and neutral wires.

Knowledge of how the devices do this is not required.

Candidates should be aware of the fact that this device operates much faster than a fuse.
 

j) Appliances with metal cases are usually earthed.

 Candidates should be aware that some appliances are double insulated, and therefore have no earth wire connection.
 

k) The earth wire and fuse together protect the wiring of the circuit.

 Candidates should have an understanding of the link between cable thickness and fuse value.