Consider the situation shown in the figure given below. If the switch is closed and then opened after some time, the circular loop adjacent to the circuit will show:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A clockwise current-pulse and then an anticlockwise current-pulse
By Lenz’s law the current induced in the loop opposes the change in magnetic flux through it. A current is induced only while the current in the circuit is changing.
Reading the figure: the longer plate of the cell is on the left, so the conventional current flows clockwise in the rectangular circuit, downwards in its right-hand arm next to the loop. By the right-hand rule this current produces a field out of the page at the loop.
Switch closed: the current grows from zero, so the outward flux through the loop increases. The induced current opposes this by producing an inward field inside the loop, so it flows clockwise.
Switch opened: the current falls to zero, so the outward flux decreases. The induced current now tries to maintain it by producing an outward field, so it flows anticlockwise.
So the loop shows a clockwise current-pulse followed by an anticlockwise current-pulse.