Question

an electric bulb is rated 220 volt and hundred watt what it is operated on 110 volt the power consumed will be what

Answer 1

P = V2/R  

If V = 220 V we have

100 W = 2202/R

R = 2202/100 Ω = 484 Ω. This is the resistance of the bulb.

When V = 110 V, power consumed =  V2/R = 1102 /484 = 25 W.