The above diagram shows a strong bar magnet moved towards the coil PQ along its axis, in the direction shown by the arrow. Which option correctly shows the momentary deflection of magnetic needle N1 and the direction of current through the galvanometer?
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Reason — As the magnet moves towards the coil, the magnetic flux linked with the coil PQ changes, so an e.m.f. is induced in it and a momentary current flows through the galvanometer. This is electromagnetic induction.
By Lenz's law, the direction of the induced current is such that it opposes the cause producing it. Here the south pole of the magnet approaches the end Q, so the end Q of the coil must itself become a south pole in order to repel the approaching south pole. Consequently the other end P of the coil becomes a north pole, and the induced current flows from P to Q through the galvanometer.
Since the end P near the needle now behaves as a north pole, it repels the north pole of the magnetic needle N1, so the needle is deflected away from the coil.