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A small conducting circular loop B has its centre on the axis of a larger circular loop A, and the planes (axes) of the two loops are mutually perpendicular. The current in loop A, which is anticlockwise when viewed from the side of B, begins to increase. What is the induced current in loop B?

1. An induced current flows in loop B, clockwise when viewed from above B
2. An induced current flows in loop B, anticlockwise when viewed from above B
3. A current is induced in loop B but its direction cannot be determined
4. No current is induced in loop B

Correct answer: No current is induced in loop B

Solution

The magnetic field produced by loop A at the location of B is directed along A's axis. Since the axes of A and B are mutually perpendicular, this field lies in the plane of loop B, so the flux of A's field through loop B is zero. Even though A's current is changing, the flux linkage with B stays zero, so dPhi/dt = 0 and no EMF/current is induced in B.

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