Name: Working of Galvanometer
Uploaded: 2019-07-19
Duration: 9 min 22 s
Description: A galvanometer is a device used to indicate the presence, direction or strength of a small electric current. Let's study the working principle and applicatio...

Question

Explain the construction and working of an electric motor.

Accepted Answer

Electric motors involve rotating coils of wire which are driven by the magnetic force exerted by a magnetic field on an electric current. When a rectangular coil is placed in a magnetic field and current is passed through it, a motor operates. The coil is subjected to a force that causes it to rotate continually. A magnetic field is created around the rectangular coil when electric current is conducted through it. 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.

Embibe Experts Solutions for Chapter: Effects of Electric Current, Exercise 1: Maharashtra Board-2019

Embibe Experts Science and Technology Solutions for Exercise - Embibe Experts Solutions for Chapter: Effects of Electric Current, Exercise 1: Maharashtra Board-2019

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