Generators and Alternators

An electric generator converts mechanical energy into electrical energy using electromagnetic induction. The principle, discovered by Michael Faraday, states that a changing magnetic field through a coil induces a voltage across it. In a generator this change is produced by rotating a coil within a magnetic field, or by rotating magnets past stationary coils, so that the magnetic flux linking each winding rises and falls and drives current through the connected circuit.

Most large generators produce alternating current and are properly called alternators. As the rotor turns, each conductor passes alternately near north and south poles, so the induced voltage reverses direction periodically, giving a sinusoidal output whose frequency depends on rotational speed and the number of magnetic poles. Direct-current generators, or dynamos, add a commutator that mechanically reverses the connections at the right moments to deliver current in a single direction.

Generators range from the alternator that charges a car battery to the massive machines in power stations driven by steam, water or wind. The same induction principle also explains electric motors, which run the process in reverse by turning electrical energy into motion, and many machines can act as either. Interactive animations are often used to illustrate how rotating coils, magnetic poles and the resulting waveform relate, making the otherwise abstract idea of induced voltage easier to grasp.

Frequently asked questions

What principle do generators rely on?

Electromagnetic induction: a magnetic field changing through a coil induces a voltage, as described by Faraday's law.

What is the difference between an alternator and a dynamo?

An alternator produces alternating current directly, while a dynamo uses a commutator to deliver direct current.

How is a generator related to an electric motor?

They are reverse processes. A generator turns mechanical motion into electricity, while a motor turns electricity into motion, and many machines can do either.