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Question
Explain the construction and working of an electric motor.
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Solution
1) Armature coil: A large number of turns of insulated copper wire wound on the iron core in rectangular a shape forms an armature coil ABCD as shown in figure
2) Strong magnet: The armature coil is placed in between two pole pieces (N and S) of a strong magnet. This provides a strong magnetic field
3) Split ring commutator: It consists of two halves (R1 and R2) of a metallic ring. The ends of the
armature coil are connected to these rings. Commutator reverses the direction of current in the armature coil.
4) Brushes: Two carbon brushes B1 and B2 are used to press the commutator.
5) Battery: The battery supplies the current to the armature coil.
Working of the electric motor:
When current is passed through the coil ABCD, arms AB and CD experience force. According to Fleming’s left-hand rule, the force experienced by arm AB is in the downward direction and arm CD in the upward direction. Both these forces are equal and opposite. This force rotates the coil in the anticlockwise direction until the coil is vertical. At this position, the contact between commutator and brushes break. So the supply to the coil is cut off. Thus no force acts on the coil. But the coil does not stop due to inertia. It goes on rotating until the commutator again comes in contact with the brushes B1 and B2. Again, the current starts passing through the coil and the arm AB rotates through 90°, 180°, 270° and 360 degrees. Now the force acting on arm AB is upward and arm CD is downward. Again this force moves the coil in the anticlockwise direction.
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