Question

A coil ABCD mounted on an axle is placed between the poles N and S of a permanent magnet as shown in Fig. 10.28

(a) In which direction will the coil begin to rotate when current is passed through the coil in direction ABCD by connecting a battery at the ends A and D of the coil?

(b) Why is a commutator necessary for continuous rotation of the coil?

(c) Complete the diagram with commutator, ets. For the flow of current in the coil?

Answer 1

a)The coil begins to rotate in anticlockwise direction.

(b) This is because, after half rotation, the arms AB and CD get interchanged, so the direction of torque on coil reverses. To keep the coil rotating in same direction, commutator is needed to change the direction of current in the coil after each half rotation of coil.