Question

$B_1$, $B_2$ and $B_3$ are the three identical bulbs connected to a battery of steady e.m.f. with key $K$ closed. What happens to the brightness of the bulbs $B_1$ and $B_2$ when the key is opened?

• A. Brightness of the bulb, $B_1$ decreases and that of $B_2$ increases.
• B. Brightness of the bulbs $B_1$ and $B_2$ decreases.
• C. Brightness of the bulbs $B_1$ increases and that of $B_2$ decreases
• D. Brightness of the bulbs $B_1$ and $B_2$ increases.

Answer 1

Answer: (A)

When key $K$ is opened, bulb $B_{2}$ will not draw any current from the source, so that terminal voltage of source increases. Hence, power consumed by bulb increases, so light of the bulb becomes more. The brightness of bulb $B_{1}$ decreases.