Joyce Podorsky, age 10, of Caplay, Penna., for her question:
How do factories get power from a dam?
A dam is a mighty wall built across a river. It stops the river from flowing along and a lake or reservoir gathers behind the dam. The dam is fitted with spillways, huge faucets that can be turned, on and off. The water can be let out of the reservoir and through the dam as needed. The spillways are near the top of the dam and the water from the reservoir spills down to the river below. It is this falling water which provides the power to make electricity.
Turn on the faucet in your bathroom and hold a piece of cardboard under the falling water. The cardboard will bead, for falling water has the power to move things. The water falling through the spillways of the dam is strong enough to move machinery. And the machinery placed there for it to move is electric generators. These are machines which create or generate electricity.
Three things are necessary for the generator to create electricity. There must be coils of copper wire. There must be a magnet. And there must be movement. A magnet gives off a magic force around it. This is called the magnetic field. Evan a toy magnet has a small magnetic field. When a needle comes within this smell magnetic field it is pulled towards the toy magnet. And the magnet in the generator is no toy. It is a monster with a very powerful magnetic field.
Ordinary magnets tend to wear out or waste their force. The electromagnet is fed by a current of electricity. It is a met^1 bar wrapped in coils of wire carrying electric current. And it can be turned on and off.
Electricity is generated when copper passes through a magnetic field, The first generator was small enough to fit into a shopping bag. It was a horseshow magnet and a round copper plate. There was a handle to turn the copper plate around. As it turned it passed between the two ands of tie horseshoe. It moved through a magnetic field. Copper wire led off and back again to the little generator in a loop or circuit. When the dandle was turned, an electric current flowed through the wire circuit.
The copper plate, moving through the magnetic field, made the electricity for this little generator. knd that is just how electricity is made in a big generator. The job of the falling water is to keep the machinery turning.
In some generators the copper coils move. In others the magnet moves. In any case electricity is made when the copper cuts through the magnetic field. The falling water turns the machinery like a water wheel.
Copper wires lead from the generator to carry the electricity where it is needed. Great pylons carry the power from the dam to factories and homes. The electric current, created by the falling water, is used to turn machinery and light the darkness.