Electric motor.

Ans. A device which converts electrical energy into mechanical energy is called an electric motor.

Principle: - Electric motor works on the principle that a current carrying conductor placed in a magnetic field experiences a force.


i.                     Armature coil: - A large number of turns of insulated copper wire wound on iron core in rectangular shape forms an armature coil ABCD as shown in the above figure.
ii.                   Strong magnet: -The armature coil is placed in between two pole pieces (N and S) of a strong magnet. This provides a strong magnetic field.  
iii.                 Split ring commutator: - It consists of two halves (R1 and R2) of a metallic ring. The ends of the armature coil are connected to these rings. Commutator reverses the direction of current in the armature coil.
iv.                 Brushes: - Two carbon brushes B1 and B2, used to press the commutator.
v.                   Battery: - The battery supplies the current (D.C.) to the armature coil.

Working: -

i.                     When current is passed through the coil ABCD, arms AB and CD experience force. According to Fleming’s left hand rule the force experienced by arm AB is in the downward direction and arm CD in the upward direction.
ii.                   Both these forces are equal and opposite. This force rotates the coil in clockwise direction until the coil is vertical.
iii.                 At this position, the contact between commutator and brushes break. So the supply to the coil is cut off. Thus no force acts on the coil.
iv.                 But the coil does not stop due to inertia. It goes on rotating until the commutator again comes in contact with the brushes B1 and B2.
v.                   Again the current starts passing through coil and the arm AB rotates through 900, 1800, 2700 and 3600. Now the force acting on arm AB is downward and CD is upward. Again this force moves the coil in clockwise direction.
vi.                 Thus, the coil rotates with the help of electrical energy. The coil of DC motor continues to rotate in the same direction.  

Uses of DC motor:

i.                     These motors are used in domestic appliances like mixers, blenders, refrigerators and washing machines.
ii.                    These motors are used in electric fans, hair dryers, record players, tape recorders and blowers.

iii.                  These motors are used in electric cars, rolling mills, electric cranes, electric lifts and electric trains.