Magnetic flux

Magnetic flux is the amount of magnetic field perpendicular to a surface, passing through that surface. Changing magnetic flux creates an electromotive force, which will often make electric current flow through a wire.

A full treatment of this subject is necessary to understand the internal workings of electric generators, but the physics and mathematics behind magnetic flux are beyond the scope of this encyclopedia and take years of study to understand properly. An excellent place to start is hyperphysics, but D. J. Griffiths' Introduction to Electricity and Magnetism is an excellent text on the subject.