Electric Motor

Question 1 What is an electric motor?

Question 2 On what principle does electric motor works?

Question 3 Explain the construction of electric motor?

Question 4 Give commercial use of electric motor?

Question 5 Give uses of D.C. motor?

Electric Motor


It converts electrical energy into mechanical energy.

Principle

A current carrying conductor placed perpendicular to magnetic field experiences a force.

Construction

1)Armature coil:It consist of a single loop of an insulated copper wire in the form of a rectangle.

2)Strong field magnet:Armature coil is placed between 2 pole pieces of a strong magnet which provide strong magnetic field.

3)Split ring type commutator:It consist of 2 halves of a metallic ring.The two ends of armature  coil are connected to these 2 halves of ring.Commutators reverses the direction of current in armature coil.

4)Brushes:Two carbon brushes press against the commutator.These brushes act as contact between commutator and terminal battery.

5)Battery:It is connected across the carbon brushes.It supplies current to the armature coil.


Working

1)When current flow through coil,arm AB and CD experience magnetic force.

2)According to Fleming’s Left hand rule,arm AB of coil experiences force in downward direction and arm CD experiences force in upward direction.

3)Both these forces are equal and opposite.

4)2 equal and opposite forces acting at different position of armature constitute a couple.

5)The couple rotate the coil in clockwise direction until the coil is in vertical position.

6)At this position,the contact of commutator and brushes break.

7)Supply of current to coil is cut off.Hence no force acts on arms of coil.But coil goes on rotating due to inertia of motion of coil until commutator again comes in contact with brushes.

8)When commutators comes in contact with brushes after rotation,direction of current in arm AB and CD is reversed.

9)The force acting on arm AB is in downward direction and force acting on arm CD is in upward direction.These 2 equal and opposite forces constitute a couple.this couple rotate coil again in clockwise direction.

10)The coil of d.c. motor continues to rotate in same direction.Hence electrical energy is converted into mechanical energy.

The commercial motor uses

1)Electromagnet in place of permanent magnet.

2)A soft iron core on which coil is wound.


Uses of D.C. motor

It is used in electric cars,rolling mills,electric cranes,lifts,drilling machine,fan,hair dryers,blowers,tape recorder,refrigerators,washing machine,mixers,blenders.

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