Electric motors and generators are used to convert the mechanical energy into electrical, and also the opposite, by electromagnetic means. It is classified as generator or dynamo the machine that converts mechanical energy into electric and from electric motor to machine that does the opposite.
The simple dynamo-electric machine is the disc dynamo that was developed by Faraday, from a mounted copper disc so that the part of this disc lies between the center and the edge of the two poles of a horseshoe magnet. The magnetic field of a permanent magnet is strong enough to run a motor.
Two physical principles are the basis of the operation of generators and motors, the first being the induction principle discovered in 1831 by Faraday. It moves through the magnetic field, or is in the vicinity of a driving circuit whose intensity can vary.
The opposite principle was verified in 1820, by André Marie Ampère. If a current passes through a driver within a magnetic field, it will exert a mechanical force on that driver.