Name: An Elementary Study of Domestic Electric Circuits
Uploaded: 2019-07-19
Duration: 5 min 52 s
Description: The electricity we consume is produced through electromagnetic induction at power plants. In this video, we will see the journey of electricity from the powe...

Question

With a labelled diagram, describe the working of an electric motor.

Accepted Answer

An electric motor is a rotating device that converts electrical energy to mechanical energy. An electric motor, as shown in the figure, consists of a rectangular coil $ABCD$ of insulated copper wire. The coil is placed between the two poles of a magnetic field such that the arm $AB$ and $CD$ are perpendicular to the direction of the magnetic field.

The ends of the coil are connected to the two halves $P$ and $Q$ of a split ring. The inner sides of these halves are insulated and attached to an axle. The external conducting edges of $P$ and $Q$ touch two conducting stationary brushes $X$ and $Y$ , respectively.

Current in the coil ABCD enters from the source battery through conducting brush $X$ and flows back to the battery through brush $Y$ . Notice that the current in arm $AB$ of the coil flows from $A$ to $B$ . In arm $CD$ it flows from $C$ to $D$ , that is, opposite to the direction of current through arm $AB$ . On applying Fleming’s left hand rule for the direction of the force on a current-carrying conductor in a magnetic field, we find that the force acting on arm $AB$ pushes it downwards while the force acting on arm $CD$ pushes it upwards.

Thus the coil and the axle $O$ , mounted free to turn about an axis, rotate anti-clockwise. At half rotation, $Q$ makes contact with the brush $X$ and P with brush $Y$ . Therefore the current in the coil gets reversed and flows along the path $DCBA$ . A device that reverses the direction of flow of current through a circuit is called a commutator. In electric motors, the split ring acts as a commutator. The reversal of current also reverses the direction of force acting on the two arms $AB$ and $CD$ . Thus the arm $AB$ of the coil that was earlier pushed down is now pushed up and the arm $CD$ previously pushed up is now pushed down. Therefore the coil and the axle rotate half a turn more in the same direction. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and to the axle.

With a labelled diagram, describe the working of an electric motor.

Important Questions on Magnetic Effects of Electric Current

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