As shown in the figure, two parallel wires carry a current I in opposite directions, and this current is decreasing. A rectangular loop is centered between the wires. The direction of the induced current through the resistor R is
A) from a to b.
B) from b to a.
C) No current is induced.

Question

As shown in the figure, two parallel wires carry a current I in opposite directions, and this current is decreasing. A rectangular loop is centered between the wires. The direction of the induced current through the resistor R is 
A) from a to b. 
B) from b to a. 
C) No current is induced.

Quizplus · Accepted Answer

According to Lenz's law, the direction of the induced current is such that it opposes the change that produced it. In this case, the decreasing current in the two parallel wires will induce a current in the loop to try to maintain the status quo. Since the induced current must create a magnetic field that opposes the decreasing magnetic field of the two wires, the induced current must flow in the same direction as the current in the wire located to the right of the loop, which is from b to a. Therefore, the correct choice is B.

As Shown in the Figure, Two Parallel Wires Carry a Current