30.16: Electric Generator: Alternator

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.

Electric generators convert mechanical energy into electrical energy. One of the  examples is the simple alternator, which consists of a conducting loop rotating with constant angular velocity, placed inside a constant uniform magnetic field.

As the loop rotates, the magnetic flux through the loop changes. Here, the angle between the area vector and the magnetic field is a product of angular velocity and time. Faraday's law gives the induced emf because of the loop rotation.

The magnetic flux and the induced emf vary sinusoidally with time. When the magnetic field and the area vector are perpendicular, the magnetic flux is zero, but the induced emf is either maximum or minimum.

Similarly, magnetic flux is maximum and minimum when the magnetic field and area vector are parallel and antiparallel, resulting in zero induced emf.

The induced emf for an alternator can be maximized by enlarging the uniform magnetic field, area of the loop, and angular velocity. 

Alternators can be used as a source of current in external circuits with the help of two slip rings and brushes.