Principle Of Operation
The scientific principle on which generators operate was discovered almost simultaneously in about 1831 by the English chemist and physicist, Michael Faraday, and the American physicist, Joseph Henry. Imagine that a coil of wire is placed within a magnetic field, with the ends of the coil attached to some electrical device, such as a galvanometer. If the coil is rotated within the magnetic field, the galvanometer shows that a current has been induced within the coil. The magnitude of the induced current depends on three factors: the strength of the magnetic field, the length of the coil, and the speed with which the coil moves within the field.
In fact, it makes no difference as to whether the coil rotates within the magnetic field or the magnetic field is caused to rotate around the coil. The important factor is that the wire and the magnetic field are in motion in relation to each other. In general, most DC generators have a stationary magnetic field and a rotating coil, while most AC generators have a stationary coil and a rotating magnetic field.