Q 12-03-214JEE MainJEE Main 2021 (26 Aug, Shift 2)Easy
An electric bulb of $500$ W at $100$ V is used in a circuit having a $200$ V supply. Calculate the resistance $R$ to be connected in series with the bulb so that the power delivered by the bulb is $500$ W.
Answer: (C) $20\ \Omega$
Bulb resistance $= \dfrac{100^2}{500} = 20\ \Omega$; rated current $= \dfrac{500}{100} = 5$ A.
With $200$ V supply: $\dfrac{200}{20 + R} = 5 \Rightarrow R = 20\ \Omega$.
Solution by Sreeraj P, M.Sc Physics