Faraday discovered that whenever a change in magnetic lux is associated with a coil of wire a voltage is induced in that cod. The value of the induced e.m.f. is proportional to the number of turns and the rate of change of magnetic flux in webers per second,
A# e = N-volts
Alternating voltages of any desired value may be obtained by using the transformer which employs this principle. Voltages need to be changed between the points of generation and the consumer several times in order to arrive at the most economical levels for transmission and distribution. Generation is carried out at voltages between 11 kV and 25 kV whilst major transmission voltages are 275 kV and 400 kV in the UK. Domestic consumers are suppled at about 240 V.