Question

A, B in the figure are identical lamps. What changes occur in the brightness of the lamps when its switch S in closed?

• A. brightness of A increases but that of B decreases
• B. brightness ofA remains the same but that of B decreases
• C. brighness of both A and B decreases
• D. brightness of A increases but that of B remains the same

Answer 1

The correct option is A brightness of A increases but that of B decreases

A and b are identical lamps

In total current of circuit will pass through A bulb

After closing switch S, equivalent resistance across circuit gets decreased and value of total current increased.

Total current increases that's why brightness of A increases.

But current gets diviced into B and C.

That's why brightness of bulb B gets decreased because brightness is proportional to current.