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

Explanation

Resistance of bulb `R= (V^2)/P =((220)^2)/(100) =22xx22 = 484 Omega`
Power consumed by the bulb when connected to mainsline
`P =(V_1^2)/(R) = (110xx 110)/(484) =25 watts`