Alternating current An electric current in which the flow of electrons changes direction regularly. It is produced in power stations, and is useful because its voltage can be changed easily by a transformer.

Circuit breaker A switch that cuts the flow of electricity round a circuit if too much current flows through it. Unlike a fuse, it can be used again.

Current electricity Electricity that flows from one point to another, for example along metal wires. The flow of current is measured in amperes, or amps (A).

Direct current An electric current that always flows in one direction. This type of current is produced by batteries.

Electrical appliance A device that converts electricity into another form of energy. For example, a light bulb converts electricity into light; an electric motor converts electricity into movement.

Electrical power The rate at which electricity does work. It is measured in watts.

Electric grid A network that supplies electricity from power stations to homes, factories and businesses. The electricity flows along insulated power cables.

Electricity A form of energy. The electricity we use is produced in power stations. It is sent out via a grid of cables to homes and businesses, where wires direct it to individual rooms. When an electrical appliance is plugged in and switched on, an electric current runs through the appliance and makes it work. This converts electricity into other sorts of energy, such as light, sound, heat or movement.

Electric motor A device that turns electric current into rotary (spinning) movement. When electricity flows through a coil of wire placed between opposite magnetic poles, the coil produces its own magnetic field. The two magnetic fields interact, pushing opposite sides of the coil in opposite directions and making it spin.

Electromagnet A temporary magnet produced by sending an electric current along a wire. Electromagnetism is used to make generators and electric motors work.

Fossil fuels Materials formed underground from the remains of dead plants and animals. The main fossil fuels are coal, oil (petroleum) and natural gas. They may be burned to provide heat, to power engines (such as internal combustion engines) or to generate electricity in power stations.

Fuse A length of wire that melts to stop the flow of electricity round a circuit if too much current flows through it.

Generator A device that turns rotary (spinning) movement into electric current. It consists of a magnet surrounded by a coil of wire. When the magnet spins, it produces a current in the wire. Generators are used to produce electricity in power stations.

Geothermal power Electricity generated by heat from inside the Earth. Geothermal power stations pump water deep underground, where it boils and rises as steam, which is used to drive turbines.

Hydro-electric power Electricity generated by moving water. Water flows from behind a dam, rushes downhill through turbines and turns generators.

Hydrogen power Power generated either by burning hydrogen to produce heat, or, in a process which does not involve burning, using it in fuel cells to generate electricity.

Mains electricity The electricity that is supplied to lights and sockets in buildings such as homes and offices.

Nuclear power Electricity generated by splitting the nuclei (cores) of uranium atoms, a process called fission. This produces huge amounts of energy, used to heat water and drive steam turbines.

Power cables Thick wires along which electricity is sent from place to place, supported by pylons or laid underground.

Power station A place where mains electricity is generated. Many are thermal power stations that use heat to boil water, producing steam which powers turbines and drives a generator.

Solar power Electricity generated from the light and heat energy of the Sun, via solar cells or a thermal power station. Solar power is renewable energy.

Space-based solar power (SBSP) A new technology involving the capture of energy from the Sun in space by satellites and transferring it down to Earth using microwave beams where it is converted to electricity. Space-based solar power makes use of the fact that sunlight is brighter outside Earth's atmosphere and that, in space, shines all the time, unlike on Earth.

Substation A structure where the voltage of mains electricity is reduced before it is sent to homes and businesses.

Tidal power Electricity generated by the movement of the tides. A tidal power station, called a barrage, uses underwater turbines to drive a generator.

Transformer A device that changes the voltage of alternating current. Transformers increase the voltage of electricity as it leaves a power station and reduce it again before it enters homes.

Turbine A machine that is caused to rotate by a fluid (including liquids and gases such as steam) in order to drive a generator.

Voltage The force needed to make electricity flow. Voltage is measured in units called volts (V).

Watt The unit of power, which is a measure of how much energy is produced or used up every second. One megawatt (MW) is the equivalent of a million watts. Megawatts are used to measure energy produced by large machines, such as power stations and electric locomotives, or by events such as lightning strikes.

Wave power Electricity generated by the up-and-down movement of waves, using floating turbines.

Wind power Electricity generated by the movement of the wind. Wind turbines use the motion of the wind in order to drive a generator. A group of wind turbines is called a wind farm.

Consultant: Chris Oxlade