The rotor is an electromagnet that comprises the center of the alternator. As the name indicates, the rotor is allowed to freely rotate in the alternator. This component is sometimes referred to as the field. Two terminals, called the field terminals, are attached to the rotor and extend outside the alternator housing.
A voltage applied to these terminals energizes the rotor. Since the rotor is an energized electromagnet when this voltage is applied, the rotation of the rotor within the stator coils produce an induced emf in the stator coils according to Faraday’s Law of Induction.
Basic configuration
A rotor consists of a coil of wire wound on an iron core, and pressed on a steel shaft. An iron segment is fastened on each side of the coil assembly so that the projections or claws interlace. The ends of the rotor coil are connected to insulated slip rings mounted on the shaft and spring loaded brushes maintain contact with the slip rings at all times.
When a current is passed through the slip rings and the coil winding, it establishes a north and south pole at the ends of the iron core and the shaft. The projections then take on the same polarity as the end of the shaft on which they are mounted and this forms pairs of north and south poles around the rotor circumference.
The rotor usually has 8 to 12 poles, which are tapered to reduce noise as the rotor rotates.
Source: CDX Global & Wikipedia - en.wikipedia.org
