Consider a metal ring kept on top of a fixed solenoid (say on a cardboard) (Fig 6.5). The center of the ring coincides with the axis of the solenoid. If the current is suddenly switched on, the metal ring jumps up. Explain.

Question

Philoid · Accepted Answer

When current is suddenly switched on, the upper end becomes south-pole. By Lenz’s law the induced current produce south-pole lower side and north upper side so repelled and jumps up.