Armature, the part of an electric generator or motor that contains the main current-carrying winding. The armature usually consists of a coil of copper wire wound around an iron or steel core. The coil and core are placed in a magnetic field produced by one or more permanent magnets or electromagnets. If the armature in a generator or motor is designed to rotate, it is called a rotor; if it is a stationary part, it is called a stator.
In a generator, either the armature or the magnet is rotated by an outside force (provided by a steam or water turbine or a gasoline or diesel engine) so that the armature coil cuts the lines of the magnetic field created by the magnet. This action produces an alternating current of electricity in the coil. This alternating current is transferred through slip rings (conducting metallic rings) connected to the ends of the coil to a set of brushes (stationary strips of metal) and conducted from there to the electric circuit where it is to be used. If direct current, instead of alternating current, is desired, a commutator (a ring divided into two insulated segments) is used instead of slip rings.
In an induction motor (the most widely used type of electric motor), an alternating electric current is supplied to the motor's electromagnets. The oscillating magnetic field produced by the magnets induces a current in the armature, causing it to rotate.