http://session.masteringphysics.com/problemAsset/1072418/2/29.12.jpg A bar magne

Question

http://session.masteringphysics.com/problemAsset/1072418/2/29.12.jpg

A bar magnet is held vertically with its upper end a little bit below the center of a horizontal metal ring. The upper end of the magnet is its north pole (see Fig. 29.12). The bar magnet is now dropped. An observer views the ring from above its center. To this observer, how will the induced current in the ring behave as the magnet falls?

The current will flow counterclockwise and be increasing.
The current will flow counterclockwise and be decreasing.
The current will flow clockwise and be increasing.
The current will flow clockwise and be decreasing.
The induced current will be zero.

Explanation / Answer

The current will flow clockwise and be decreasing. Because As the magnet approaches from the top, first the south pole of the magnet induces a current in the ring and from Lenz's law a clockwise current flows in the ring and the ring behaves as a south pole so as to oppose the motion of the magnet.

Next as the magnet passes through the ring and Recedes from the ring, again the receding north pole induces a clockwise current, following Lenz's law, and the ring still behaves as a south pole, Now Attracting the magnet. Since the magnet is receding the induced current is decreasing in the circuit.

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