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Consider a metal ring kept on top of a f...

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

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There was no magnetic flux linked with the metal ring in the beginning. When the current is suddenly switched on and the direction of current is as shown in the figure the magnetic flux linked with the metal ring (downward) increases and anticlockwise current is induced in the metal ring (seen from top) this current is in opposite direction to that in the solenoid and they repel each other and the ring will move upward.
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KUMAR PRAKASHAN-ELECTROMAGNETIC INDUCTION-Section C Ncert Exemplar Solution (MCQs)
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  4. There are two coils A and B as shown in figure. A current starts flowi...

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  9. The mutual inductance M12 of coil 1 with respect to coil 2

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