Question

Two identical bulbs are connected in parallel as shown in the fig. When switch S is closed power consumed in bulb B is P. What will the power consumed by the same bulb when switch S is opened?

Answer 1

Answer:

Let each bulb has x impedance(resistance)

in first case

$r_{eq }= x + x = 2x$

So

$P = \frac{ {V}^{2} }{r} = \frac{ {E}^{2} }{2x}$

When S is closed

$r_{eq }= x+{x \over 2}= \frac{3x}{2}$

So power

$P'= \frac{ {2E}^{2} }{3x} = {4P \over 3}$