Question

A bulb of 25 W, 220 V and another bulb of 100W, 220V are connected in series with a supply line of 220 V. Then

• A. both bulbs will glow with same brightness
• B. both bulbs will get fused
• C. 25 W bulb will glow more brightly
• D. 100 W bulb will glow more brightly

Answer 1

Answer: (C)

25 W bulb will glow more brightly

Using $P=V^2/R$ the resistance of 25 W bulb is $R_{25}=\frac{{220}^2}{25}=1936\Omega$ and resistance of 100 W bulb is $R_{100}=\frac{{220}^2}{100}=484\Omega$

When they are connected in series , the same current I flow through each bulb and power , $P=I^{2}R$ or $P\propto R$

Since $R_{25}>R_{100}$ ,so 25 W bulb will glow more brightly.