An electric generator is a device used to convert mechanical energy into electrical energy.

Principle: An electric generator is based on the principle of electromagnetic induction according to which if a closed coil is rotated about an axis perpendicular to a uniform magnetic field, an induced current is produced whose direction is governed by Fleming’s right-hand rule.

Construction: An electric generator consists of a rectangular coil called armature, field magnet, slip rings and carbon brushes.

Working:

1. When the armature is rotated in clockwise direction inside the magnetic field produced by the magnets, it cuts magnetic lines of force. This changing field produces induced current in the coil whose direction is given by Fleming’s right-hand rule.
2. When the axle attached to two slip rings is rotated such that the arm AB moves up and CD downwards, induced current starts to flow from A to B and C to D. Thus, an induced current flows in the direction ABCD and in the external circuit, it flows from B, to B.
3. After half a rotation, arm CD starts moving up and AB moves down. As a result, the direction of induced current will be DCBA and begin to flow from B , to B₂ in the external circuit. Thus, after every half rotation, the polarity of the current in the respective arms changes. Such a current, which changes the direction after equal intervals of time is called an alternating current.