Question

A 25 W and a 100 W bulbs are joined in parallel and connected to A.C. mains. Which will glow brighter?

Answer 1

We know that P = V²/R or R = V²/P.

\(\frac{R_{25}}{R_{100}} = \frac{P_{100}}{P_{25}} = \frac{100}{25} \) = 4

Power dissipated,

\(\frac{P'25}{P'100} = \frac{I^2R_{25}}{I^2R_{100}} = \frac{R_{25}}{R_{100}}\) = 4

Bulb of 25 W will glow brighter and will consume power 4 times more than 100 W bulb.