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.
Construction:
ELECTRIC MOTOR
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.