MAGNETIC EFFECTS OF ELECTRIC CURRENT
ELECTRIC MOTOR
It is a rotating device that converts electrical energy to mechanical energy.
It is used in electric fans,
refrigerators, mixers, washing machines, computers, MP3 players etc.
An
electric motor consists of a rectangular coil ABCD of insulated copper
wire. It is placed between the two poles of a magnetic field such that the arm
AB and CD are perpendicular to the direction of the magnetic field.
The ends of the coil are
connected to the two halves P & Q of a split ring.
Inner sides of halves are insulated and attached to an axle. The external
conducting edges of P & Q touch two conducting stationary brushes X
& Y.
Current
from the source battery enters the coil ABCD through conducting brush X and
flows back to the battery through brush Y. The current in arm AB (from A to B)
and arm CD (from C to D) is in opposite direction.
On
applying Fleming’s left-hand rule, the force acting on arm AB pushes it down
while the force acting on arm CD pushes it up. Thus, the coil & axle rotate
anti-clockwise. At half rotation, Q makes contact with the brush X and P
with brush Y. So, the current in the coil gets reversed and flows along
the path DCBA.
A
device that reverses the direction of flow of current through a circuit is
called a commutator. In electric motors, the split ring acts as a
commutator.
The
reversal of current also reverses the direction of force acting on the arms AB
and CD. Thus, the arm AB is now pushed up and the arm CD is pushed down. So,
the coil and axle rotate half a turn more in same direction. The reversing of
the current is repeated at each half rotation. Thus, the coil and axle continuously
rotate.
The commercial motors use
- An electromagnet in place of permanent magnet.
- Large number of turns of the conducting wire in the current carrying coil.
- A soft iron core on which the coil is wound. They together are called an armature. It enhances power of the motor.
