Question

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V. So what is the power consumed? ​

Answer 1

P = I * VI is the current through the resistance where the voltage is applied. Again,V=IR.So,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.