Class X Physics: Electric Motor

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Electric Motor

An electric motor is a rotating device that converts electrical energy to mechanical energy. An electric motor is used as an important component in electric fans, refrigerators, mixers, washing machines, computers etc.

Working of an Electric Motor


Parts: Magnets, rectangular copper coil, Split ring (also called commutator), Brushes

(i) An electric motor 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.

(ii) The ends of the coil are connected to the two halves of a split ring. The inner sides of these halves are insulated and attached to an axle. The external conducting edges touch two conducting stationary brushes B1 and B2, respectively.

(iii) Current in the coil ABCD enters from the source battery through conducting brush B1 and flows back to the battery through brush B2.

(iv) 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.

(v) On applying Fleming’s left-hand rule, we find that the force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards.

(vi) Thus, the coil and the axle mounted free to turn about an axis, rotate anti-clockwise. At half rotation, C2 makes contact with the brush B1 and C1with brush B2. Therefore, the current in the coil gets reversed and flows along the path DCBA.

(vii) A device that reverses the direction of flow of current through a circuit is called a commutator. The split ring acts as a commutator.

(viii) The reversal of current also reverses the direction of the force acting on the two arms AB and CD. Now, the arm AB is now pushed up and the arm CD is 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.

 

Commercial Motors

In commercial motors

(i) an electromagnet in place of a permanent magnet is used;

(ii) there is a large number of turns of the conducting wire in the current carrying coil; and

(iii) a soft iron core for winding the coil is used. The soft iron core, on which the coil is wound, plus the coils, is called an armature. This enhances the power of the motor.

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