Electric Motor

These notes are based on the chapter Magnetic Effect of Electric current class 10 science NCERT book and CBSE syllabus.

Electric motor is a device which converts electrical energy into mechanical energy.

Principle of Electric Motor

Electric motor works on the basis of rule suggested by Marie Ampere and Fleming’s Left Hand Rule. You may recall that Fleming's Left Hand Rule tells about the direction of force generated when there is interaction between magnetic field and electric field. Such an interaction produces a field which is responsible for generating rotation in the motor shaft.

Structure of Electric Motor

In an electric motor, a rectangular coil is suspended between the two poles of a magnetic field.
The electric supply to the coil is connected with a commutator.
Commutator is a device which reverses the direction of flow of electric current through a circuit.

Working of Electric Motor

When electric current is supplied to the coil of electric motor, it gets deflected because of magnetic field.
As it reaches the half way, the split ring which acts as commutator reverses the direction of flow of electric current.
Reversal of direction of current reverses the direction of forces acting on the coil.
The change in direction of force pushes the coil; and it moves another half turn.
Thus, the coil completes one rotation around the axle. Continuation of this process keeps the motor in rotation.

In commercial motor, electromagnet instead of permanent magnet an armature is used. Armature is a soft iron core with large number of conducting wire turns over it. Large number of turns of conducting wire enhances the magnetic field produced by armature.

Capacitor in a motor

You may have seen a capacitor attached atop the base of a ceiling fan. This looks like a small cylinder with a plastic case. Do you know what is the function of this capacitor?

A capacitor stores electrical energy in it. Capacitor supplies very high voltage of electric current to the motor. The high energy supplied by the capacitor brings the motor into motion. Once the motor attains about 75% of its optimum speed, the capacitor is switched off by a mechanism in the motor. The motor will take too much time to attain full speed in the absence of a capacitor. Hence, a capacitor is always present in most of the motors.

Uses of Electric Motor

Electric motor is used in those electrical devices which work on rotary motion of at least one of its parts. For example, the blades of ceiling fan rotate because of electric motor. Some other examples of electrical appliances with electric motor are, mixer grinder, vacuum cleaner, hard disc drive, hair dryer, CD player, etc.