A bar magnet is held stationary while a circular loop of wire is moved toward the magnet at constant velocity at position A as in the figure.
The loop passes over the magnet's center at position B and moves away from the magnet at position C.Viewing the loop from the left as indicated in the figure,for which position is the induced current zero?
A)Position A
B)Position B
C)Position C
D)The induced current is never zero.

Question

A bar magnet is held stationary while a circular loop of wire is moved toward the magnet at constant velocity at position A as in the figure. 
The loop passes over the magnet's center at position B and moves away from the magnet at position C.Viewing the loop from the left as indicated in the figure,for which position is the induced current zero?
A)Position A 
B)Position B 
C)Position C 
D)The induced current is never zero.

Quizplus · Accepted Answer

According to Faraday's Law of Induction, a changing magnetic field can induce an electric current in a loop of wire. As the loop is moved toward the magnet at position A, the magnetic field in the loop increases, creating an induced current in the opposite direction. At position B, the loop is directly above the magnet's center where the magnetic field is maximum and unchanging, so there is no change in the magnetic field and therefore no induced current. At position C, the loop moves away from the magnet, causing the magnetic field to decrease and inducing a current in the opposite direction to its motion toward the magnet. Therefore, the induced current is zero at position B.

A Bar Magnet Is Held Stationary While a Circular Loop