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

Options

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

Answer

D

Explanation

Resistance of the electric bulbs, `R = (V^2)/(P)` `(P = V^2//R)`
or `R = ((220 V)^2)/(100 W) = 484 Omega`
Power consumed by the bulb when it is operated at `110 V` is given by
`P' = (V'^2)/( R) = ((110 V)^2)/(484 Omega) = (110 xx 110)/(484) W = 25 W` `(V' = 100 V)`
Thus, (d) is the correct answer.