It is called alternator to machine what generates alternating electric current from the transformation of the mechanical energy. In order to carry out this objective, it resorts to the electromagnetic induction.
To understand how an alternator works, you first have to know what the mechanical energy. This energy consists of the sum of the Kinetic energy (given by the movement) and the potential energy (linked to the ability to develop work by virtue of the position that one has in a force field) of a body.
The kinetic energy plus the potential energy of a body, therefore, constitute the mechanical energy of the same. What an alternator does is take this energy and convert it into a alternating current.
At this point we come to another key concept. Alternating current is a electric current (flow of electric charges) whose direction of movement is periodically reversed.
To convert mechanical energy into electrical energy, the alternator uses the electromagnetic induction. This phenomenon makes it possible to produce a electromotive force in a Body that is exposed to a varying magnetic field.
If a conductor is subjected to a varying magnetic field, it induces an electromotive force (tension). The alternator, in this frame, changes polarity constantly to produce movement, and therefore, electric power.
It can be said that the alternator is a rotating machine that presents a inductor (which receives the mechanical energy of the rotation and allows the creation of the magnetic field) and a induced (the driver which is traversed by the force of the magnetic field). The most frequent use of alternators is to generate alternating current energy to supply an electrical network.