Name: Current Carrying Conductor Inside a Magnetic Field
Uploaded: 2019-07-19
Duration: 6 min 14 s
Description: A current-carrying conductor behaves as a magnet. So, will it respond when kept in a magnetic field? If yes, how so? Let's discuss in this video.

Question

Why are carbon brushes used? How do these work? In order to find answers to such questions, visit a nearby workshop and try to understand the construction of an electric motor.

Accepted Answer

The electric motor consists of a rectangular loop of copper wire having a resistive coating. As shown in the figure, it is placed between the north pole and south pole of a magnet (such as a horseshoe magnet) in such a way that its branches AB and CD are perpendicular to the direction of the magnetic field. The two ends of the loop are connected to the two halves (X and Y) of the split ring. The two halves of the ring have a resistive coating on their inner surfaces and are tightly fitted on the axle. The two halves of the split ring, X and Y, have their outer conducting surfaces in contact with the two stationary carbon brushes, (E and F), respectively.

i. Carbon brushes are used to press the split rings.
ii. The contact between the split rings and brushes result in the flow of current through the circuit.

When the circuit is completed as shown in the figure, the current flow in the branch AB of the loop from A to B through the carbon brushes E and F. Since the direction of the magnetic field is from the north pole to the south pole, according to Fleming’s left-hand rule, a force is exerted on the branch AB and pushes it down. The current in the CD branch is in the opposite direction to that in the AB branch, and therefore, a force is exerted on the branch CD in an upward direction. Thus, the loop and the axle start rotating in an anticlockwise direction. After half rotation, the two halves of the split ring X and Y come in contact with carbon brushes F and E, respectively, and the current in a loop starts flowing in the direction of DCBA changing the polarity and the direction of current. Therefore, a force is exerted on the branch DC in a downward direction and on the branch BA in the upward direction, and the loop continues to rotate in the anticlockwise direction. Thus, the current in the loop is reversed after each half rotation and the loop and the axle continue to rotate in the anticlockwise direction.

Maharashtra Board Solutions for Chapter: Effects of Electric Current, Exercise 4: Find out

Maharashtra Board Science and Technology Solutions for Exercise - Maharashtra Board Solutions for Chapter: Effects of Electric Current, Exercise 4: Find out

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