Physics P2.5

P2 5.1

Cells and batteries suppy a current which passes around the circuit in one direction; direct current.

Mains supply passes in one direction then reverses in the other direction; alternating current.

The frequency of the UK mains supply is 50 hertz, which means it changes directions 50 times a second. The voltage of the mains is 230V.

The live wire of a mains supply alternates between a positive and a negative potential with respect to the neutral wire. The neutral wire always remains at zero volts.

The live wire alternates between peak voltages of +325V and -325V. 

The frequence of an ac supply can be determined from an oscilloscope using the equation: frequency, in hertz, = 1/ time, in seconds.

P2 5.2

Lots of electrical appliances are connected to sockets using a cable and a three-pin plug. The outer cover of a three-pin plug is made of rubber and plastic, which are both good electrical insulators. The pins of the plug are brass, which conduct electricity. The earth wire is connected to the longest pin. A brown wire is connected the live pin. A blue wire is connected to the neutral pin. The green and yellow wires are connected to the earth pin.

Appliances with metal cases have to be earthed, because the case could conduct electricity. Appliances with…