Q. There are two electric bulbs of $40\ W$ and $100\ W.$ Which one will be brighter when first connected in series and then in parallel
A) $40\ W$ in series and $100\ W$ in parallel
B) $100\ W$ in series and $40\ W$ in parallel
C) $40\ W$ both in series and parallel will be uniform
D) $100\ W$ both in series and parallel will be uniform
Explanation
(a) $\frac{R_{1}}{R_{2}} = \frac{P_{2}}{P_{1}} = \frac{100}{40} = \frac{5}{2}.$ Resistance of $40\ W$ bulb is $\frac{5}{2}$ times than $100\ W.$ In series, $P = i^{2}R$ and in parallel, $P = \frac{V^{2}}{R}.$ So $40\ W$ in series and $100\ W$ in parallel will glow brighter
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.