Chapter 21- Electromagnetism | D.C Motor

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Which of the following statements about the d.c motor shown below is/are correct?

1- The motor roates in the clockwise direction
2- Increase the current through the coil can increase the turning speed of the motor
3- The motor converts mechanical energy to electrical energy

This whole question hinges on your understanding of Fleming Left Hand Rule (LHS)
If you understand the concept, you can easily solve the question, so, we shall take a look at LHS.


Firstly, remember its the LEFT hand, not the RIGHT hand.
As shown in the diagram, the forefinger( second finger) is the direction of the magnetic field ( from N->S) and the middle finger is the direction of the current.

The interaction between the magnetic field and the electric field produced by the current results in a FORCE, which is represented by the thumb.

With this knowledge, lets tackle the options one by one.

1- The motor roates in the clockwise direction.
Looking at the diagram, and LHS, what makes the motor rotate?
Yes, the force which arises due to the magnetic and electric field, so by applying the LHS, you should get the result of the force being UPWARDS ( motor nearer to S pole), hence, and a DOWNWARDS direction force for side of motor closer to N pole) Hence, a clockwise direction.

Add on : How does a upwards and downwards force translate to a clockwise direction?
Imagine at every point of the motor spinning path, there wll always be a reaction between the magnetic and electic field, and from there, you plot out the force, you will get a resultant force at different angles which when put together translates into clockwise path( This is a bit hard to explain..it is easier to explain face to face)

2- Increase the current through the coil can increase the turning speed of the motor
Increasing the current would increase strength of electric field, and conversely, the resultant force, hence making it spin faster.

3- The motor converts mechanical energy to electrical energy
No,it converts electrical energy( the current) to kinetic/ mechanical energy( spinning of motor)

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