Question

As shown in the figure, $P$ and $Q$ are two coaxial conducting loops separated by some distance. When the switch $S$ is closed, a clockwise current $I_P$ flows in $P$ (as seen by $E$ ) and an induced current $I_{Q_1}$ flows in $Q.$ The switch remains closed for a long time. When $S$ is opened, a current $I_{Q_2}$ flows in $Q.$ Then the directions of $I_{Q_1}$ and $I_{Q_2}$ (as seen by $E$ ) are

• A. Respectively clockwise and anticlockwise
• B. Both clockwise
• C. Both anticlockwise
• D. Respectively anticlockwise and clockwise

Answer 1

Answer: (D)

When switch $S$ is closed magnetic field lines passing through $Q$ increases in the direction from right to left.
So, according to Lenz's law induced current in $Q$, i.e., $I_{Q_1}$ will flow in such a direction so that the magnetic field lines due to $I_Q$ passes from left to right through $Q$.
This is possible when $I_{Q_1}$ flows in anticlockwise direction as seen by $E.$ Opposite is the case when switch $S$ is opened,
i.e., $I_{Q_2}$ will be clockwise as seen by $E$.