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 wires means that the magnetic flux through the loop is decreasing. To oppose this, the induced current must flow in a direction that produces a magnetic field in the opposite direction to the original field. By the right-hand rule, the induced field must be into the page, which corresponds to a current flowing from b to a through the resistor R. Therefore, the answer is B.

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