Question

A metallic ring is attached to the wall clock. When the north pole of a magnet is brought near the ring, the induced current in the ring is( assume axis of magnet coincides with that of ring)
A. Zero
B. in clockwise direction
C. in anti-clockwise direction
D. infinite

Answer 1

This problem is based on Lenz law and Fleming’s right rule. The Lenz’s law will be utilized to find the strength of magnetic field and Fleming’s right hand rule is used to find the direction of the induced current.

Complete step by step answer:

In figure, we will consider the front of the closed conducting loop as the region that is approaching the bar magnet. Other side we will consider as the back of the loop. When the north pole of the magnet moves towards the loop the electric flux through the loop increases because the magnet is in motion and therefore the current will be induced in the ring.

By using Lenz's law the direction of induced e m f or induced current in such a way that it opposes the changing flux that is caused by the field of the approaching magnet. Hence the induced current will circulate in such a way that magnetic field lines through the loop are directed from back to front of the loop.

Then by applying the right hand rule we can find the direction of the induced current that is by placing the thumb pointing against the magnetic field lines, which is towards the bar magnet. Your fingers wrap in an anti-clockwise direction as viewed from the bar magnet.That is, an approaching north pole induces an anti-clockwise current with respect to the magnet.

Hence, option C is correct.

Note: As there are two Fleming’s rules in magnetic effects of electric current, that is, Fleming’s left hand rule and Fleming’s right hand rule. The Fleming's left hand rule should be used to find the direction of magnetic field and Fleming’s right hand rule is used to find the direction of the induced current. Depending upon the direction of which physical quantity needs to be determined the law should be chosen.