Question

In an electric motor, the direction of current in the coil changes in every.

• A. rotation
• B. two rotations
• C. four rotations
• D. half rotation

Answer 1

The correct option is D half rotation

Answer is D.
The electric motor is one of the first machines devised to converts electrical power into mechanical power. Permanent magnet (PM) direct current converts electrical energy into mechanical energy through the interaction of two magnetic fields. One field is produced by a permanent magnet assembly, the other field is produced by an electrical current flowing in the rectangular coil ABCD, through the brushes and split-ring commutators. These two fields result in a torque which tends to rotate the coil. As the coil turns, the current in the winding is commutated to produce a continuous torque output.
The split ring commutator is made from 2 pieces of copper that are held apart in the center from touching each other. They look like a copper ring split in the middle. The function of the commutator rings is to reverse the direction of current flowing through the coil every time the coil just passes the vertical position during a revolution.
Hence, the direction of current in the coil changes in every half rotation.