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Electric Motor

A motor is a device that changes electrical energy into mechanical energy. The working of an electric motor is based on the fact that when a current is passed through a conductor placed suitably in a magnetic field, it experiences a force. 

The principle of a motor is illustrated in Figure. It consists of a rectangular coil of wire called the armature which is mounted on a spindle so that it can rotate between the pole pieces of a powerful permanent magnet. To make the continuous rotation possible. The two ends of the wire are connected to the so-called split-ring commutator made of copper. Two carbon brushes are made to press tightly against the two halves of the commutator as shown in figure. Current is passed through the coil by connecting the brushes to a battery. 





Working of the Electric Motor

Let us suppose that the coil is in horizontal position (as shown in Figure), when the current is passed through it. In the arm AB of the coil the current flows in the direction BA and in the arm CD its direction is DC. Hence, according to Fleming's left-hand rule, the arm AB will experience an upward force and CD a downward force. These two equal and opposite forces constitute a couple which rotates the coil in a clockwise direction. Suppose the coil has rotated to its vertical position, the gaps of the split rings are closely by the brushes, thus cutting off the current in the coil. 
Since the coil has acquired a momentum in reaching this vertical position, its inertia will not let it stop. If the current was not cut-off the coil will experience an anticlockwise couple, which will bring it back to its original position. The split rings prevent this. Thus, the coil continues its clockwise rotation until it becomes horizontal again. At this position, the position occupied previously by arm CD is now taken by arm AB and vice versa. The brushes move away from the gaps and the current passes through the coil again. Fleming's left hand rule tells us that the couple now acting on the coil is still clockwise Hence, the coil continues to rotate Thus, a continuous rotation of the coil is achieved. 
The rotation of the axle or spindle can be conveyed by means of the belt to any machine. Electric motors are used in industry and in domestic appliances such as in electric fans, washing machines, refrigerators, mixers, grinders, vacuum cleaners, sewing machines, etc.
The speed of rotation of the coil can be increased: 
  1. Current in the coil,
  2. Area of the coil,
  3. Number of turns in the coil, and
  4. Strength of magnetic field.

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