ELECTRIC MOTOR

 ELECTRIC MOTOR

  It works on the principle that when a current-carrying conductor is  placed in a magnetic field it will experience a force on it.

It consists of the following parts:-

1. Armature ABCD 

2. Field magnets N and S                                           

3. Split rings P and Q                                  

4. Brushes X and Y

      When a current is allowed to flow through the coil ABCD by closing the switch, the coil starts rotating in anti-clockwise direction. This happens because of a downward force acts on arm AB and at the same time, an upward force acts on  arm CD. The direction of forces can be  found by using Fleming’s left hand rule. As a result, the coil rotates in anti-clockwise direction.

      After half a rotation, the position of AB and CD gets interchanged  so the direction of current in the coil ABCD gets reversed. hence the half-ring P comes in contact with brush Y and half-ring Q comes in contact with brush Y.

      The speed of rotation of motor can be increased by:-

(i)            Increasing current through armature

(ii)          Increasing number of turns in the coil of armature

(iii)        Increasing area of the coil.

(iv)        Increasing strength of the magnetic field.

 Q 3.1: What kind of energy transformation takes place in an electric motor:-

           (a) Electrical energy into chemical energy

           (b) Electrical energy into light energy 

           (c) Mechanical energy into electric energy

           (d) Electrical energy into mechanical energy.

Q3.2. State YES or NO:-

Statement	Responses
(i)            Fleming’s left hand rule is used to find the direction of force	Yes/no
(ii)          Electric motor works on the principle of Electro Magnetic Induction	Yes/no

 

Q 3.3. Will there be any change in the direction of rotation of the armature of motor when position of both the poles (N and S)  are interchanged? Give your reply with proper explanation.

…………………………………………………………………………………………………………………………………………………………………………………………

Answer 

3.1

 Full Credit:-Option (d)

 No Credit:- For any other responses.

  3.2

Full Credit:- 

(i) Yes  (ii)No    

Answer: 3.3

 Full credit :-Direction of rotation of electric motor will change in opposite direction .It will rotate in clockwise direction because of opposite directions of forces on the arms AB and CD according to Fleming’s left hand rule due to change in direction of magnetic field.

Partial credit:-  Opposite direction

 No credit:- For any other response or  wrong responses.