Electric Motor

«Q.1 Define electric motor.

Ans.   A device which converts electrical energy into mechanical energy is called an electric motor.

Q.2      On which principle the working of an electric motor is based ?

Ans.     Electric motor works on the principle that a current carrying conductor placed in a magnetic field experiences a force.

Q. 3   With a neat diagram explain the construction & working of an electric current.

Ans.    Principle: An electric motor converts electrical energy into mechanical energy.

Construction of an electric motor :

Fig. Electric motor.

i)      Armature coil ABCD – It consist of a large number of turns of insulated copper wire wound around a rectangular iron core ABCD.

ii)      Strong magnet : The armature coil is placed between the poles of a strong magnet (N & S) to create a strong magnetic field.

iii)     Split ring commutator : A metallic ring divided into two halves (R₁ & R₂). The ends of the armature are connected to the two rings. This commutator helps to reverse the direction of the current in the armature coils.

iv)     Brushes : Two carbon brushes B₁ & B₂ are used to press upon the commutator.

v)      Battery : It supplies the current (D.C) to the armature coil.

Working of the electric motor:

i.     When a current is switched on, the armature coil ABCD, due to the action of the magnetic, the arm AB experiences a force in the downward direction & arm CD in the upward direction. These forces are equal in magnitude & opposite in direction. This force rotates the coil in clockwise direction until it becomes vertical.

ii.     In this position, the contact between the commutator & the brushes  breaks & the supply of current to the coil is cut off. Hence, no force acts on the coil. But the coil continues to rotate due to the principle of inertia.

iii.    The commulator again comes in contact with the brushes. The current once again passes through the coil. This sets the arm AB in rotation. As the arm AB completes one rotation from 90⁰  to 360⁰, downwards & the arm CD moves upwards. This force again moves the coil in a clockwise direction.

iv.     Thus, the electrical energy helps the coil to rotate in the same direction. Hence, the coil of the motor continues to move in the same direction & the electrical energy of DC is converted into mechanical energy.

Q.4      Give the uses of DC motor Or  Explain the applications of a DC motor.

Ans.     Uses/ applications of a DC motor.

1.     These motors are used in domestic appliances like mixtures, blenders, refrigerators & washing machines.

2.      These motors are used in electric fans, hair dryers, record players, tape recorders & blowers.

3.      These motors are used in electric cars, rolling mills, electric cranes, electric lifts & electric trains, etc.

Q. 5     What is the characteristic feature of a magnetic levitation train?

Ans.  In the case of a magnetic levitation train, the currents passing through the electromagnets in the railway track & on the train produce magnetic fields that make the train ‘float’ above the rails & propel is forward.

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