An electric motor is a device which converts electrical energy into mechanical energy. Electric motors are crucial in modern life. ey are used in water pump, fan, washing machine, juicer, mixer, grinder etc. We have already seen that when electric current is passed through a conductor placed normally in a magnetic field, a force is acting on the conductor and this force makes the conductor to move. is is harnessed to construct an electric motor.
To understand how a motor works, we need to understand how a current carrying coil experiences a turning effect when placed inside a permanent magnetic field and it is shown in Figure 3.16.
In Fig. 3.16, a simple coil is placed inside two poles of a magnet. Now look at the current carrying conductor segment AB. The direction of the current is towards B, whereas in the conductor segment CD the direction is opposite. As the current is owing in opposite directions in the segments AB and CD, the direction of the motion of the segments would be in opposite directions according to Flemingâ€™s le hand rule. When two ends of the coil experience force in opposite direction, they rotate.
If the current flow is along the line ABCD, then the coil will rotate in clockwise direction first and then in anticlockwise direction. If we want to make the coil rotate in any one direction, say clockwise, then the direction of the current should be along ABCD in the first half of the rotation and along DCBA in the second half of the rotation. To change the direction of the current, a small device called split ring commutator is used (Fig. 3.18).
When the gap in the split ring commutator is aligned with terminals X and Y there is no flow of current in the coil. But, as the coil is moving, it continues to move forward bringing one of the split ring commutator in contact with the carbon brushes X and Y. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil.
The speed of rotation of coil can be increased by:
i. increasing the strength of current in the coil.
ii. increasing the number of turns in the coil.
iii. increasing the area of the coil and
iv. increasing the strength of the magnetic field.