How does a generator turn motion into electricity?

A generator converts mechanical energy into electrical energy. A turbine, engine or another source of motion turns part of the machine. Many generators rotate a magnetic field inside stationary coils of conducting wire, while other designs move the coils. The important change is the magnetic flux through each coil: a measure of the magnetic field passing through its enclosed area.

When this flux changes, an electric voltage is induced around the coil. A faster change or more turns can produce a larger voltage. If the coil connects to a closed external path, the voltage can drive current through a load. The wire already contains charges; the generator does not manufacture electrons.

A magnet by itself does not provide an endless supply of electrical energy. Delivering electrical power creates a magnetic effect that opposes the change producing it, consistent with Lenz’s law. The driving source must therefore do mechanical work. A loaded generator generally requires more driving effort than an otherwise similar unloaded one, and real machines also transfer some energy as heat.

As a rotor keeps turning, the flux and induced voltage usually vary, producing alternating current in many designs. An unchanging flux produces zero induced voltage, even though a magnetic field may still be present. A generator therefore needs a changing magnetic situation, a suitable conducting path and a continuing energy input to deliver power.