Question

An electric bulb is rated 220 volt - 100 watt. The power consumed by it when operated on 110 volt will be :

• A. 75 watt
• B. 40 watt
• C. 25 watt
• D. 50 watt

Answer 1

Answer: (C)

25 watt

Answer 2

Resistance of electric bulb $R=\frac{V^{2}}{P}$ where subscripts denote for rated parameters. $R=\frac{\left(220\right)^{2}}{100}$ Power consumed at 110 volt, $P_{consumed}=\frac{V^{2}}{R}$ $\therefore P_{consumed}=\frac{\left(110\right)^{2}}{\left(220\right)^{2}/100}=25\,W$