Question

A light bulb has the rating 100 W, 220 V. If the supply voltage is 110 V, then power consumed by the bulb is

• A. 50 W
• B. 75 W
• C. 25 W
• D. 20 W

Answer 1

The correct option is C 25 W

$P=\frac{V^2}{R}$

If $V=220$ V we have

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

$R=\frac{{220}^2}{100}\Omega =484\Omega$. This is the resistance of the bulb.

When $V=110$ V, power consumed $=\frac{V^2}{R}=\frac{{110}^2}{484}=25$ W.

So, 25 W power is consumed when it is operated on 110 V.