Question

Write a short note on:
(1) Armature Coil
(2) Brushes
(3) Commutator
(4) Direct Current

Answer 1

Hint
A generator converts mechanical energy into electrical energy. An AC generator converts mechanical energy into electrical energy in the form of alternating current whereas a DC generator converts mechanical energy into electrical energy in the form of direct current. Construction of both types of generators is based on a similar design consisting of armature coil and carbon brushes. However, a DC generator consists of commutators while an AC generator consists of slip rings.

Complete step by step answer
The working of a generator is based on the principle of electromagnetic induction. Some parts of a generator are described briefly.
(1) Armature coil: Armature coil in generators consists of several turns of perfectly insulated copper wire wound over a soft iron core. The armature is mounted on a rotor shaft and the ends of it are connected to an external circuit through rings and carbon brushes. The uniform magnetic field is provided by a permanent magnet and the rotational axis of the coil is normal to the field.
(2) Brushes: Carbon brushes are used in generators to reduce wear and tear of slip rings in ac generators and commutators in dc generators. Carbon brushes leave fine particles on the surface of the rings on rubbing thereby working as lubricants. This results in the reduction of friction between the rings and brushes.
(3) Commutator: A DC generator consists of two rings split in half called commutators. The commutators are used to change the direction of current and reverse its polarity in the windings of the armature after the armature coil comes across the magnetic field neutral axis.
(4) Direct current: Direct current is the type of electric current that is in one direction and does not change periodically unlike alternating current.

Note
Care should be taken while describing the type of rings used in the two types of generators. The rings split in half i.e. commutators present in a DC generator are also called split rings. That must not be confused with the slip rings present in an AC generator.