Question

A 25 W, 220 V bulb and a 100 W, 220 V bulb are connected in series across a 220 V line; which electric bulb will glow more brightly?

• A. $25W$ bulb
• B. $100W$ bulb
• C. Both will have equal incandescence.
• D. Neither will give light.

Answer 1

Answer: (A)

$25W$ bulb

Resistance of 25 W bulb is $R_{25}=V^2/P=(220{)}^2/25=1936\Omega$

Resistance of 100 W bulb is $R_{100}=V^2/P=(220{)}^2/100=484\Omega$

As both bulbs are in series, current through them will be the same. But

resistance of 25 W bulb is more. Hence, from the relation $P=I^{2}R$, the 25 W bulb will glow more brightly.