Principle of Electric Motor

Current carrying conductor if placed in magnetic field experiences a magnetic force which causes Motion of the conductor. The direction of force on the conductor can be determined using Fleming’s Left hand rule. It is given as
Stretch the forefinger middle finger and thumb such that they are mutually perpendicular to each other. If forefinger points in direction of magnetic field and middle finger in the direction of current then thumb will point in the direction of the force acting on the conductor i.e. direction of motion of conductor.

Basic construction of Electric motor

Armature Coil: An Armature coil is made up of large number of turns of insulated copper wire wound on iron core. In the figure, ABCD is a armature coil.
Strong Magnet: Armature coil is placed between the two poles of strong magnet. Magnet provides strong Magnetic Field to the coil.
Split rings or commutator: It is a Metallic ring like structure consisting of two halves P and Q. the two halves are connected to two ends of armature coil. Commutator is mounted on Axle through insulation and is free to rotate.
Brushes: Two carbon brushes X and Y are pressed on commutator rings and used to provide electric current to the coil.
Battery: Battery supplies electric current to the coil.

Working of Electric motor

• When current flows through the coil ABCD, the arms of the armature coil ABCD experiences force . The direction of force and the direction of motion of conductor can be obtained by using Fleming’s Left hand rule.
• The direction of current in branch AB of electric motor is opposite to that of direction of current through CD hence force acting on both arms is equal and opposite. Force acting on AB is such that it tend to move the arm AB downwards while the force on CD tend to move arm CD upward. Due to which AB move downwards while CD moves upwards causing rotation of coil ABCD. In case of arm BC and AD since current is either parallel or antiparallel to magnetic force hence there is no force acting on these branches.





• When the coil of electric motor becomes vertical, contact between commutator and brushes break but the coil continue to rotate as it is in motion .
• Commutator again comes in contact with brushes and current starts flowing again, but this time the direction of current through the arms reverses. Now force acting on AB is in upward direction and on CD it is in downward direction.
• Rotation of coil causes rotation of axle. Such rotations continues till electrical supply to the coil is on. This is how the motor works.

Uses of electric motor

• It is used in Domestic Appliances such as Mixer, Blender, Refrigerator, and Washing Machine.
• It is also used in Hair Dryers, Electric Fan, Record Players, Tape Recorders and Blowers.
• It is also used in electric cars, Rolling mills, electric cranes, Electric lifts and Electric trains.

Modifications in commercial Motors

• In commercial motors instead of permanent magnet an electromagnet is used. electromagnet is a device that produces magnetic field when current is supplied to it.
• Instead of single turn commercial motor consists of large number of turns so as to form coil. Often commercial electric motor use soft iron core on which the coil is wound. This enhances power of the motor due to stronger force acting on it.

This article is helpful for Class 10 Science

Keywords: Electric motor, Fleming’s Left hand rule, Principle of Electric Motor, Working of Electric motor

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