Same as problem 4 except the coil A is made to rotate about a vertical axis (Fig 6.3). 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

Question

Philoid · Accepted Answer

First of all understand the Lenz’s law According to this law, the direction of induced e.m.f. or current in a circuit is such that it opposes the cause of flux change accordance with the law of conservation of energy.

(negative shows oppose the cause).

At t=0 as mention in question current in B is clockwise and considered coil A above coil B. The current flowing in counterclockwise in B is equivalent to north-pole of magnet and magnetic field lines are emanating upward to coil A. When coil A start rotating at t=0, the current in A is constant along clockwise direction accordance with Lenz’s law.

So all options are wrong except (a).

Therefore, option (a) is correct answer.