Physics
A coil ABCD mounted on an axle is placed between the poles N and S of a permanent magnet as shown in figure.
(a) In which direction will the coil begin to rotate when current is passed through the coil in direction ABCD by connecting a battery between the ends A and D of the coil?
(b) Why is a commutator necessary for the continuous rotation of coil?
(c) Complete the diagram with commutator, etc. for the flow of current in the coil.
Electro-Magnetism
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Answer
(a) The coil begins to rotate in anticlockwise direction, when current is passed through the coil in direction ABCD by connecting a battery between the ends A and D of the coil.
(b) A commutator is necessary for the continuous rotation of coil because the arms AB and CD get interchanged after half rotation, so the direction of torque on coil reverses. To keep the coil rotating in the same direction, a commutator is needed to reverse the direction of current in the coil after each half rotation of coil.
(c) Completed diagram with commutator showing the flow of current in the coil is given below:
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