Question

A coil is wound on an iron rod and connected to an ac source as shown in fig. Two more coils AB and CD are also wound on the same rod. If ends B and C are joined, a filament bulb connected between ends A and D glows well. However, if B and D are joined and the bulb is connected between A and C, it glows feebly. This shows that

(a) coils AB and CD are in series in first case while they are in parallel in the second case

(b) in the second case, the two coils are in phase addition and then have unequal turns

(c) in the second case, the two coils are in phase opposition and they have equal turns

(d) in the second case, two coils are in phase opposition and they have unequal turns

Answer 1

Correct option (d) in the second case, two coils are in phase opposition and they have unequal turns

Explanation:

B,C are joined and bulb is connected between A, D: current is flowing through both the coils in the same direction. The two coils are in phase.

B,D are joined and bulb is connected between A, C: current is flowing in opposite direction in the coils. The two coils are in phase opposition. The current does not become zero as the number turns are different causing different magnitudes of induced emf.