Explain the working of electric motor with a neat diagram.

Explanation

1) Consider a rectangular coil kept in a uniform magnetic field as shown in figure.
2) Switch on the circuit , so that the current flows through the rectangular coil . The direction of current is shown in the figure.
3) The sides AB and CD of the coil are always at right angles to the magnetic field.
4) According to right hand rule, at AB the magnetic force acts inward perpendicular to the field of magnet and on CD, it acts out ward.
5) The top view of coil is shown in the figure.
6) The force on the sides BC and DA varies because they make different angles at different positions of the coil in the field. At BC, magnetic force pulls the coil up and at DA magnetic force pulls it down.
7) The net force acting on AB and CD is zero because they carry equal currents in the opposite direction. SImilarly the sum of the forces on sides BC and DA is also zero. So, net force to zero on the coil.
8) But the rectangular coil comes into rotation in clockwise direction because equal and opposite pair of forces acting on the two sides of the coil.
9) IF the direction of current in the coil is unchanged. It rotates, upto half rotation in one direction and the next half in the direction opposite to previous like to and fro motion.
10) IF the direction of current in the coil is changed the coil will rotate continuously in one and the same direction.
11) To achieve this, brushes `B_1` and `B_2` are used.
12) These brushes are connected in the battery. The ends of the coil are connected to the battery The ends of the coil are connected to slip rings `C_1` and `C_2` which rotate along with the coil.
13) Initially `C_1` is in contact with `B_1` and `C_2` is in contact with `B_2`.
14) After half rotation, the brushes come into contact with the other slip rings in such away that direction of current through the coil is reversed. This happens every half rotation.
15) Thus the direction of rotation of the coil remains the same. This is the principle used in electric motor.
16) In electric motors electrical energy is converted into mechanical energy.