Shaylea Beloe of Henley Primary School asks :-

How does electricity heat up the water from our tap?

Pat Bodger, an electrical engineer at the University of Canterbury, responded.

Electricity is the word used to describe energy in the form of moving charges. In metal wires, the charges are small ball-like things called electrons. They are pushed back and forth by a changing force we call "voltage". They have lots of energy. They rub up against the much larger atoms of the wire and transfer some of their energy. The wire gets hot. Thus, electric energy gets converted to heat energy. Its a bit like you rubbing a tennis ball fast over the surface of a metal plate.

In your home, a voltage is applied to a special wire, called an element, placed inside a tank of water, called a cylinder. The element is made of a metal wire which has a lot of resistance to movement of the electrons, so it gets very hot. The heat generated is transferred to the water and its temperature rises. An electric jug works the same way.

When you turn your hot water tap on, initially cold water sitting in the pipe between the cylinder and the tap comes out. After a while the hot water from the cylinder reaches you. If you don't use the tap for a while, the water in the cylinder heats to a set temperature. The electricity is then turned off by a temperature detecting switch called a thermostat, otherwise the water would boil.