Q. Two bulbs consume same power when operated at 200 V and 300 V respectively. When these bulbs are connected in series across a DC source of 400 V, then the ratio of power consumed across them is
A) 2/3
B) 3/2
C) 4/9
D) 9/4
Explanation
(c) $R = \frac{V^{2}}{P}\ or\ R \propto V^{2}\ \therefore\frac{R_{1}}{R_{2}} = \frac{(200)^{2}}{(300)^{2}} = \frac{4}{9}$.
When bulbs are connected in series, the current $I$ is same through each. As $P = I^{2}\ R\ or\ P \propto R(\ as\ I$ is same in series),
so $\frac{P_{1}}{P_{2}} = \frac{R_{1}}{R_{2}} = \frac{4}{9}$.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.