What do we use to turn electricity on and off?

We need electricity to help us live. Most of our machines contain circuits and need at least some electricity. Computers, phones, televisions, cars, trains, airplanes - they all use electricity. Machines that use very small amounts of electricity are called electronic machines. But the whole country uses massive amounts of electricity. Most of this electricity is produced in power stations. It is carried round the country in metal wires, or conductors. These are fixed to great big, tall utility poles.