Question

Two electric bulbs, rated at (25 W, 220 V) and (100 W, 220 V), are connected in series across a 220 V voltage source. If the 25W and 100 W bulbs draw powers $P_1$ and $P_2$ respectively then__________?

• A. $P1=9W,P2=16W$
• B. $P1=4W,P2=16W$
• C. $P1=16W,P2=4W$
• D. $P1=16W,P2=9W$

Answer 1

Answer: (C)

$P1=16W,P2=4W$

$R_1=\frac{{220}^2}{25}=1936\Omega$

$R_2=\frac{{220}^2}{100}=484\Omega$

$i=\frac{220}{R_1+R_2}=\frac{1}{11}A$

$P_1=i^2{R}_1=\frac{1}{121}\times 1936=16W$

$P_2=i^2{R}_2=\frac{1}{121}\times 484=4W$