In the figure, two solenoids are side by side. The switch S, initially open, is closed. 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 solenoids are side by side. The switch S, initially open, is closed. 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

When the switch S is closed, the current in the left solenoid starts increasing from zero. This increasing current induces a magnetic flux in the right-hand solenoid in a direction that opposes the increase in current. By the right-hand grip rule, the induced magnetic field is directed into the page.
This induced magnetic field then induces an emf in the right-hand solenoid, causing a current to flow from b to a, opposing the increase in the left-hand solenoid current. Therefore, the induced current through the resistor R is in the same direction as the current from b to a, which is from b to a.

In the Figure, Two Solenoids Are Side by Side