Same as problem 4 except the coil A is made to rotate about a ver… - Vidyadip

MCQ

Same as problem 4 except the coil A is made to rotate about a vertical axis (Fig). No current flows in B if A is at rest. The current in coil A, when the current in B (at t = 0) is counterclockwise and the coil A is as shown at this instant, t = 0, is:

A
Constant current clockwise.
B
Varying current clockwise.
C
Varying current counterclockwise.
D
Constant current counterclockwise.

✓

Answer

Constant current clockwise.

Solution:

Key concept: In this problem, the Lenz’s law is applicable so let us introduce Lenz’s law first.

Lenz's law gives the direction of induced emf/induced current. According to this law, the direction of induced emf or current in a circuit is such as to oppose the cause that produces it. This law is based upon law of conservation of energy.

When the current in coil B (at t = 0) is counter-clockwise and the coil A is considered above it. The counter clockwise flow of the current in coil B is equivalent to north pole of magnet and magnetic field lines are eliminating upward to coil A. When coil A starts rotating at t = 0, the current in A is constant along clockwise direction by Lenz's rule.

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