In the figure, two parallel wires carry currents of magnitude I in opposite directions. A rectangular loop is midway between the wires. The current I is decreasing with time. The induced current through the resistor R is
A) from a to b.
B) from b to a.
C) There is no induced current through the resistor.

Question

In the figure, two parallel wires carry currents of magnitude I in opposite directions. A rectangular loop is midway between the wires. The current I is decreasing with time. The induced current through the resistor R is 
A) from a to b. 
B) from b to a. 
C) There is no induced current through the resistor.

Quizplus · Accepted Answer

According to Lenz's law, the direction of the induced current is in such a way as to oppose the change in magnetic flux causing it. Here, the decreasing current in the wires creates a magnetic field in the direction perpendicular to the plane of the rectangular loop, and it is decreasing with time. To oppose this decrease, the induced current in the loop should flow in a direction such that it creates a magnetic field in the opposite direction. This can be achieved by the induced current flowing counterclockwise in the loop, i.e., from point a to point b. Therefore, the answer is choice A.

In the Figure, Two Parallel Wires Carry Currents of Magnitude