A permanent bar magnet with the south pole pointing downward is dropped through

Question

A permanent bar magnet with the south pole pointing downward is dropped through a solenoid, as shown in the illustration. What is the direction of the induced current that would be measured in the ammeter as the magnet falls completely through the solenoid? up down first down, then up first up, then down If the magnet, still oriented with the south pole pointing downward, is pulled upward completely through the solenoid, what is the direction of the induced current measured in the ammeter? down first down, then up up first up, then down

Explanation / Answer

a) According to Lenz law

Current induced in the coil always opposes the causes due to which it is induced

So it will induce in such a way that it opposes the motion of magnet

So top end will behave like a south pole

Current flows intially upwards and when magnet leaves the other end current changes its direction and moves downwards

So answer is 4th option

FIRST UP THEN DOWN

b) Now if magnet is moving upwards

then the direction of induced current is will be same as that of previous case as the motion is magnet retrace its previous path

Hence answer is again 4th option

FIRST UP, THEN DOWN

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