A bar magnet is dropped from above and falls through the loop of wire shown below. The north pole of the bar magnet points downward towards the page as it falls. Which statement is correct?
A) The current in the loop always flows in a clockwise direction.
B) The current in the loop always flows in a counterclockwise direction.
C) The current in the loop flows first in a clockwise, then in a counterclockwise direction.
D) The current in the loop flows first in a counterclockwise, then in a clockwise direction.
E) No current flows in the loop because both ends of the magnet move through the loop.

Question

A bar magnet is dropped from above and falls through the loop of wire shown below. The north pole of the bar magnet points downward towards the page as it falls. Which statement is correct? 
A) The current in the loop always flows in a clockwise direction. 
B) The current in the loop always flows in a counterclockwise direction. 
C) The current in the loop flows first in a clockwise, then in a counterclockwise direction. 
D) The current in the loop flows first in a counterclockwise, then in a clockwise direction. 
E) No current flows in the loop because both ends of the magnet move through the loop.

Quizplus · Accepted Answer

As the magnet falls through the loop, a current is induced in the loop due to the changing magnetic field. The direction of the induced current follows Lenz's Law, which states that the induced current will always flow in a direction to oppose the change in magnetic field that induced it. As the north pole of the magnet approaches the loop, it induces a magnetic field in the loop that is upward, so the induced current flows counterclockwise to produce a magnetic field downwards to oppose the upward change in magnetic field. As the north pole of the magnet moves away from the loop, it induces a magnetic field in the loop that is downward, so the induced current flows clockwise to produce a magnetic field upwards to oppose the downward change in magnetic field. Therefore, the current in the loop flows first in a counterclockwise, then in a clockwise direction. Choice D is the correct answer.

A Bar Magnet Is Dropped from Above and Falls Through