Question

Two bulbs marked ‘A’ (60W, 220V) & ‘B’ (100W, 220V) are connected in parallel to 220 volt source. Which of the two will glow brighter?

• A. Bulb B
• B. Bulb A
• C. Same brightness
• D. ‘A’ glows ‘B’ does not

Answer 1

The correct option is A Bulb B

When voltage is constant then $P=\frac{V^2}{R}$
$P\propto \frac{1}{R}$ so when $R\uparrow ,power\downarrow andvice-versa$
$BulbA:P=\frac{V^2}{R}\Rightarrow R_a=\frac{V^2}{P}=\frac{{220}^2}{60}=806$
$BulbB:P=\frac{V^2}{R}\Rightarrow R_a=\frac{V^2}{P}=\frac{{220}^2}{100}=484$
$So{R}_B<R_A$
$\Rightarrow P_B>P_A$
Which means more power in bulb B and hence it will glow brightly