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 IP flows in P (as seen by E) and an induced current IQ1 flows in Q. The switch remains closed for a long time. When S is opened, a current IQ2 flows in Q. Then, the directions of IQ1 and IQ2 (as seen by E) are
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → anticlockwise and clockwise, respectively
By Lenz’s law, the current induced in Q opposes the change in the magnetic flux through Q. The loops are coaxial, so the field of P threads Q along the common axis. By the right-hand rule, a current that is clockwise as seen by E produces a field through the loops pointing away from E.
Switch closed: the current in P rises from zero, so the flux through Q, directed away from E, increases. The induced current in Q must produce a field towards E, so IQ1 is anticlockwise as seen by E.
Switch kept closed: the current in P is steady, the flux does not change, and no current is induced in Q.
Switch opened: the current in P falls to zero, so the flux through Q, directed away from E, decreases. The induced current tries to maintain it by producing a field away from E, so IQ2 is clockwise as seen by E.