As shown in the figure, a battery supplies a steady current to the solenoid on the left. The two solenoids are moving toward each other with speeds v. 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, a battery supplies a steady current to the solenoid on the left. The two solenoids are moving toward each other with speeds v. 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 in magnetic flux. As the two solenoids are moving towards each other, the magnetic flux through the solenoid on the right increases. Therefore, the induced current through the resistor R would create a magnetic field in the opposite direction, i.e. from a to b, to oppose the increase in magnetic flux through the solenoid on the right.

As Shown in the Figure, a Battery Supplies a Steady