|BSAK Physics Department||
You need to know about mains electricity:
a) Cells and batteries supply current that always passes in the same direction. This is called direct current (d.c.).
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.
f) The structure and wiring of a three-pin plug.
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).
j) Appliances with metal cases are usually earthed.
k) The earth wire and fuse together protect the wiring of the circuit.
And you also need to know about charge and power:
a) When an electrical charge flows through a resistor, the resistor gets hot.
b) The rate at which energy is transferred by an appliance is called the power.
P= E / t
c) Power, potential difference and current are related by the equation:
P = I x V
d) Energy transferred, potential difference and charge are related by the equation:
E = V x Q
e) the structure of an electric cable for a three prong plug has the three wires individually insulated and coloured, and then they are surrounded by further insulation.