Question

# What is an electric motor? With the help of a labelled diagram, described the working of a simple electric motor.

Solution

## Electric motor is a device used for converting electrical energy into mechanical energy. Working of an electric motor.Initially the coil $$ABCD$$ is in the horizontal position. On passing the switch, current enters the coil through carbon brush $$P$$ and commutator half ring $$X$$. The current flow in the direction $$ABCD$$ and leaves via ring $$Y$$ and brush $$Q$$. The direction of magnetic field is from $$N$$ pole to $$S$$ pole of the magnet. According the Fleming's left-hand rule, the force on sides $$AB$$ and $$CD$$ is in the downward and upward direction respectively. This makes the coil $$ABCD$$ move in the anticlockwise direction.When the coil reaches vertical position, then the brushes $$P$$ and $$Q$$ will touch the gap between the two commutator rings and current is cut off. But the coil does not stop rotating as it has already gained momentum. When the coil gas beyond the vertical position, the side $$CD$$ comes on left side and side $$AB$$ come to right side, and the two commutator rings change contact from one brush to the other. This reverses the direction of current in the coil which in turn reverses the direction of force acting on the sides $$AB$$ and $$CD$$ of the coil. The side $$CD$$ is pushed down and side $$AB$$ is pushed up. Thus, the coil rotates anticlockwise by another half rotation.The reversing of current in the coil is repeated every half rotation due to which the coil (and its shaft) continuous to rotate as long as current from the battery  is passed through it. The rotating shaft of electric motor can drive a large number of machines which are connected to it.Physics

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