question_answer 46)

  In the arrangement shown in figure, there are two coils wound on anon-conducting cylindrical rod. Initially, the key is not inserted. Then the key is inserted and later removed. Then (a)The deflection in the galvanometer remains zero throughout (b) There is a momentary deflection in the galvanometer but it dies out shortly and there is no effect when the key is removed. (c) There are momentary galvanometer deflections that die out shortly, the deflections are in the same direction. (d) There are momentary galvanometer deflections that die out shortly, the deflections are in opposite directions. Thus the galvanometer shows momentary deflections in opposite directions.

Answer:

                    (d) In the above arrangement, whenever an electric current through the first coil is changed, an emf is induced in the coil due to change in magnetic field lines which pass through the neighboring second coil. When key is inserted and removed, then the magnetic field lines passes through second coil increases and decreases in two cases respectively. Therefore, the direction of current in two cases is in opposite directions. Thus the galvanometer shows momentary deflections in opposite directions.