Question

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed is:

• A. $100W$
• B. $75W$
• C. $50W$
• D. $25W$

Answer 1

The correct option is D

$25W$

We know that
$Power=\frac{V^2}{R}$
So if at 220V bulb consumes 100W,

$\Rightarrow 100=\frac{{220}^2}{R}$

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

But when it is operated at 110V,

$Powerconsumed=\frac{{110}^2}{R}$

= $\frac{{110}^2}{484}$

$=25W$

$\therefore$The power consumed by the bulb is equal to $=25W$.