Question

Two electric bulbs one rated 40 W-200 V and other 100 W -200 V are connected in a house wiring circuit. Which one of the following statement about them is correct?

• A. The resistance of the filaments in both the bulbs are same
• B. The resistance of filament in 40 W bulb is more than the resistance of 100 W bulb
• C. The resistance of the filament in 100 W bulb is more than the resistance of 40 W bulb
• D. None of the above

Answer 1

Answer: (B)

We know that, $P=\frac{V^2}{R}$ $\Rightarrow$ $R=\frac{V^2}{P}$ $\therefore$ $R_1=\frac{V_1^2}{P_1}$ $=\frac{{(200)}^2}{40}=1000\Omega$ and $R_2=\frac{V_2^2}{p_2}=\frac{{(200)}^2}{100}=400\Omega$ So, the resistance of filament of bulb of 40 W is greater than that of 100W.