Electric generators induce an emf by rotating a coil in a magnetic field. A simple alternator is an AC generator that creates electrical energy that varies sinusoidally with time. A simple alternator consists of a conducting loop that is placed inside a uniform magnetic field. The loop is connected to split rings connected to the external circuit with the help of brushes.

The magnetic flux passing through the coil varies sinusoidally as the loop rotates inside the magnetic field. This sinusoidally changing magnetic flux induces an emf that also varies sinusoidally. For the instant when the rate of change of the magnetic flux passing through the coil is zero, the induced emf is either at maximum or minimum. On the other hand, when the rate of change of the magnetic flux is at maximum or minimum, the induced emf is zero. The sinusoidally varying induced emf generates an induced current that also varies sinusoidally. The magnitude of the induced emf can be increased by increasing the magnetic field strength, the angular velocity of the rotation, the area of the loop, or the number of loops.

In real life, alternators are used in the automobile industry with slightly different designs. In automobiles, the loop stays stationary, but the electromagnets rotate around the loop. The alternators are used for the ignition, lights, and entertainment systems in vehicles.