発電機: オルタネーター

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.