ELECTRICITY TRANSMITION
UK mains electricity is A.C., it has a R.M.S. voltage of about 240 V, and has a frequency that is fixed at 50 Hz. A.C. is used because it can be transformed up and down easily. After it is generated the voltage is stepped up about 400 000 V, it is transmitted across the country like this as it means only a small current is required to transmit a large amount of energy, and the smaller the current the less the loss of energy in transmission wires (given by I² R).