Draw a neat labelled diagram of electric motor and write its principle.

Principle: When a current-carrying rectangular coil is placed in a magnetic field, it experiences a force (couple) and rotates. An electric motor converts electrical energy into mechanical energy.

Diagram (electric motor):

             B ___________ C
              |           |
     _____    |   coil    |    _____
    |     |   |  ABCD     |   |     |
    |  N  |   |           |   |  S  |
    |_____|   |___________|   |_____|
   magnet    A      |      D   magnet
   pole            axle
                 __|__
                ( R1 R2 )  ← split ring commutator
              B1 |     | B2 ← carbon brushes
                 |     |
                 |__ + | - ___( key )__|
                    battery

Labels: magnetic poles N and S, rectangular coil ABCD, axle, split rings R₁ and R₂ (commutator), carbon brushes B₁ and B₂, battery, key; arrows show the direction of current in the coil and the direction of rotation.

Working: current enters the coil through brush B₁ and ring R₁. In arm AB and arm CD the current flows in opposite directions, so by Fleming’s left hand rule one arm is pushed up and the other down; the two forces form a couple and the coil rotates. After every half rotation the split rings exchange their contact with the brushes, so the direction of current in the coil reverses and the coil keeps rotating in the same direction. The rotating axle is used to run fans, mixers, pumps and other machines.