If you’ve ever moved paper clips around with a magnet, or arranged metal filings into a beard on a ‘Wooly Willy’ toy as a child, then you have already lifted the lid on one of the basic principals behind the operation of an a/c generator; the movement of electrons.
Materials that conduct electricity (conductors) are made up of atoms with ‘free electrons’. Move a magnet towards a paper clip and it attracts the free electrons in the clip, this is the reason you can pick the paper clips up with a magnet. By contrast, the atoms which make up materials such as wood and rubber do not have any free electrons and do not conduct electricity (insulators), which is why your magnet won't pick up a tooth pick. Very simply, a generator is a device which moves a magnet near a collection of copper wires to create a steady flow of those free electrons.
It may help you to imagine a generator as acting like a pump pushing water through a pipe. Only instead of pushing water, the generator uses magnets to push free electrons along copper wiring, resulting in an electrical supply. A water pump moves a certain number of water molecules and applies a certain amount of pressure to those water molecules. Likewise, a generator moves a certain number of electrons and applies a certain amount of pressure to those electrons. In an electrical circuit, the number of electrons being pushed is called the amperage or current and the pressure pushing the electrons along is called the voltage. This analogy is something of an over simplification but should help you paint a picture of the properties at work in a generator.
The generator is based on the principle of "electromagnetic induction" discovered in 1831 by Michael Faraday, a British scientist. Faraday discovered that if an electric conductor, like a copper wire, is moved through a magnetic field, electric current will flow (or "be induced") in the conductor. So the mechanical energy of the moving wire is converted into the electric energy of the current that flows in the wire.
The two main parts of a generator can be described in either mechanical or electrical terms:
· Rotor: The rotating part of a generator.
· Stator: The stationary part of a generator.
· Armature: The power-producing component of generator. The armature windings generate the electrical current. In a/c generators, the armature is normally on the stator.
· Field: The magnetic field component of generator. The magnetic field of the generator can be provided by either electromagnets or permanent magnets. In a/c generators the field coils are normally mounted on the rotor.
If you would like to find out more about the science of electricity, or if your child needs reference material for a school project related to electricity, the U.S. Energy Information Administration has a wonderful site providing a great introduction which can be found here.