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Questions
Explain the construction and working of the following. Draw a neat diagram and label it.
Electric motor
Explain the construction and working of electric motor in short.
Solution
- Construction: Electric motor consists of the following parts:
- Rectangular coil: A large number of turns of insulated copper wire wound on iron core in rectangular shape forms a coil ABCD as shown in following figure.
- Strong magnet: The coil is placed in between two pole pieces (N and S) of a strong horse shoe magnet which provides a strong magnetic field. The sides AB and CD are perpendicular to the direction of the magnetic field.
- Split ring: It consists of two halves of a metallic ring (X and Y). The ends of the coil are connected to these rings. The outer conducting surfaces of spilt rings X and Y are in contact with the two stationary carbon brushes. Spilt rings reverse the direction of current in the coil.
- Brushes: Two carbon brushes E and F are used to press the split rings.
- Axle: The two halves of the rings have a resistive coating in their inner surfaces and are tightly fitted on the axle. The main function of an axle is to rotate with the coil.
- Battery: The battery supplies the current to the coil.
- Working:
- When the circuit is completed, the current passes through the brush E from A to B in branch AB.
- As, the magnetic field acts from north pole to south pole, according to Fleming’s left-hand rule, the force experienced by arm AB is in the downward direction and arm CD is in the upward direction.
- Both these forces are equal in magnitude and opposite in direction and hence, the coil rotates in an anticlockwise direction.
- After half rotation, the split rings X and Y come in contact with brushes E and F respectively.
- Again the current starts passing through the coil in opposite direction.
- The force acting on branch BA is upward and DC is downward, this force again moves the coil in an anticlockwise direction.
- This shows that the current in the loop ABCD is reversed after every half rotation, and the loop continues to rotate in the same direction.
- Thus, the coil rotates with the help of electrical energy.
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