Magnetic Effects of Electric Current | Class 10 CBSE | Web Notes | Part 4: Electric Motor
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 arms AB and CD are perpendicular to the direction of the magnetic field.
The ends of the coil are connected to the two halvesP & 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.
A simple electric motor
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 and 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 pushed up and the arm CD is pushed down. So, the coil and axle rotate half a turn more in the same direction. The reversing of the current is repeated at each half rotation. Thus, the coil continues to rotate continuously.
The commercial motors use:
An electromagnet in place of the field.
Large number of turns in the solenoid.
A soft iron core on which the coil is wrapped. Together with the solenoid, they are called an armature. This enhances strength of the field.
