Question

Same as problem 4 except the coil A is made to rotate about a vertical axis (figure). 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 ______.

Options

• constant current clockwise.

• varying current clockwise.

• varying current counterclockwise.

• constant current counterclockwise.

Answer 1

Same as problem 4 except the coil A is made to rotate about a vertical axis (figure). 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 constant current clockwise.

Explanation:

 In this problem, 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 coil A is considered above it. The counterclockwise flow of the current in coil B is equivalent to north pole of magnet and magnetic field lines are eliminated upward to coil A. When coil A starts rotating at t = 0, the current in A is constant along a clockwise direction by Lenz’s rule.