Two metallic rings A and B, identical in shape and size but of different resistivities Pa and Pb are kept of the top of two identical vertical solenoids. When current I is switched on in both the solenoids in an identical manner, the rings A and B jump to heights ha and hb resp, with ha > hb. What are the possible relations between their resistivities and their masses ma and mb?
The Attempt at a Solution
Let us assume that the current in the two solenoids is towards right (as seen from a side) and anticlockwise as seen from the top.
The anticlockwise flow of current at the top creates a north pole there. The magnetic field through the solenoid is directed outwards which induces a clockwise current in the ring. As seen from the bottom, the flow of current in the ring creates a south pole.
The north pole of the solenoid and the south pole of the ring attract each other. Why will the ring jump?