CBSE Class 10 Answered

The principle of electric motor:

The electric motor works on the principle of force experienced by a current carrying conductor in a magnetic field.
Two forces of equal magnitude act in opposite direction on the two parallel sides of coil. Since they act along different lines they cause rotational motion.

Construction:
1.  A coil of wire wound around an axle is placed between the two poles at the magnets.
2.  The two ends of coil abcd are connected to the two terminals of a battery through split ring commutators C1 and C2and brushes B1 and B2.

Working:
1. As the current flows through coil in anticlockwise direction (d  c  b  a), the force is experienced by arms ba and dc.
2. Applying Fleming's left hand rule, ba experiences a force upwards and dc experiences a force downwards.
3. The coil abcd experiences two parallel, equal and oppositely directed forces. The coil rotates in clockwise direction about its axle.
4. Split rings C1 and C2 move along with the coil. After half the rotation of the coil, C1 and C2 get interchanged. C1 is now in touch with Brush B2 and C2 is now in touch with brush B1. (See Fig. (ii) of electric motor.)
5. The direction of the current in the coil continues to be anticlockwise. However on comparing the two fig., the direction of current in arms ab and cd has reversed.
6. ab part of the coil experiences a downward force and cd experiences an upward force. The coil continues its clockwise motion under the effect of these opposite, equal and parallel forces.
7. Thus the electrical energy from the battery has been converted into the continuous mechanical rotational motion of the coil in a motor.