Draw a Labelled Diagram of an Electric Motor, Principle and Worki Exercise Chapter 13 Magnetic Effect of Current

Q. No 11: Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?
Ans: An electric motor is a device which converts electrical energy into mechanical energy. The principle behind the electric motor is based on Fleming’s left hand rule.

Working: When a current is allowed to flow through the coil PQRS the coil starts rotating anti-clockwise. This happens because a downward force acts on length PQ and at the same time, an upward force acts on length RS. As a result, the coil rotates anti-clockwise.
Current in the length PQ flows from P to Q and the magnetic field acts from left to right, normal to length PQ. Therefore, according to Fleming’s left hand rule, a downward force acts on the length PQ. Similarly at an upward force acts on the length RS. These two forces cause the coil to rotate anti-clockwise.
When coil complete half rotation, the position of PQ and RS interchange. The half-ring D comes in contact with brush A and half-ring C comes in contact with brush B. therefore the direction of current in the coil PQRS gets reversed. Now the current flows through the coil in the direction SRQP.

The direction of current through the coil PQRS reverse after every half rotation. As a result, the coil rotates in same direction. The split rings help to reverse the direction of current in the circuit. These are called the commutator.