Question

In a DC electric motor, a pair of split rings is used as a commutator. True/False?
(A) True
(B) False

Answer 1

Hint: In an electric motor, the magnet is fixed hence direction of the magnetic field remains constant. When a coil is placed in a magnetic field, it experiences torque to align its magnetic moment in the direction of the magnetic field.

Complete step by step solution:
In an electric motor, since the direction of the magnetic field remains constant. And the coil experiences torque to align its magnetic moment in the direction of magnetic field, the direction of magnetic moment must change after the coil aligns its magnetic moment in the direction of magnetic field. This change in direction of current can either be achieved by providing an AC supply, in which current changes direction periodically, or by using split rings as a commutator so that direction of current changes in the coil, although direction of current remains the same through the supply, as in case of DC supply.

Hence in case of a DC motor, a pair of split rings are used as a commutator.

Therefore, the correct answer to the question is option : A

Additional information: An electric generator can also give AC or DC output. After each rotation the direction of current changes in the coil rotating between the magnets. To get an AC output, the output can be taken as it is, so slip rings are used. And to get a DC output, the output terminals should be reversed periodically, hence a split ring commutator is used.
The function of a split ring commutator is to change the terminals periodically.

Note: To understand the working of Electric motors and generators, students should not study them separately. Instead both AC and DC type of generator as well as motor should be studied together and one should only remember the difference in their constructions. Along with the difference, we should also understand the need of those different parts used according to the required output.