NCERT Class 10: Science Learning Concepts

Science: Chapter 13-Magnetic Effects of Electric Current-Concepts

13.4 Electric Motor

The force generated due to magnetic field explained in the previous section is used to rotate a axle fixed to the current wire and thus construct a electric motor.

Working of a DC motor:

Let’s see how a simple DC motor works .

 Figure 6 : A simple DC Motor

In the above figure we have placed a rectangular coil ABCD inside a permanent magnet. By convention magnetic field lines are drawn from north pole(N) to south pole(S). Terminals A and B of the coils are attached to two split rings P and Q. When the coil rotates spilt rings P and Q also rotates. We have connected a DC voltage source to two stationary brushes X and Y. Current will flow from the positive terminal of the voltage source to the negative terminal through the brushes and the coil.

Current in arm AB flows in opposite direction to the current in arm CD. If we apply Fleming’s left hand rule in both arms we will find that in arm AB force is pushing the coil downwards and in arm CD force is pushing the coil upwards. These two opposite forces will rotate the clock anti-clockwise. After half a turn the coil AB and CD will change their position .Contacts with split ring Q will be to the brush X and contacts with split ring P will be to the brush Y. Now force on AB will be upwards, force on CD will be downwards and that will rotate the coil for next half.