A circular coil of copper wire is lying flat on a horizontal table. A bar magnet is held with its south pole downward, vertically above the center of the coil. The magnet is released from rest and falls toward the coil. As viewed from above, you can say that, as it falls, the magnet induces
A) counterclockwise current in the loop.
B) clockwise current in the loop.
C) no current in the loop.
D) an emf but no electric current in the loop.
E) Not enough information is provided.

Question

Quizplus · Accepted Answer

As the magnet falls towards the center of the coil, the magnetic field lines of the magnet cut through the coil. This changing magnetic flux induces an emf (electromotive force) in the coil in accordance with Faraday's law of electromagnetic induction. The direction of the induced current can be determined using Lenz's law, which states that the induced current will flow in a direction to oppose the change in magnetic flux that produced it. In this case, the induced current creates a magnetic field that opposes the motion of the falling magnet. Therefore, the current in the coil must produce a magnetic field that is directed upward, which can only occur if the current flows clockwise when viewed from above.

A Circular Coil of Copper Wire Is Lying Flat on a Horizontal