An electric bulb is rated 220 V and 100 W. Calculate the power consumed when it is operated on 110 V.

Explanation

We have `P= (V^(2))/(R)`
or `100= ((220)^(2))/(R)` …(1)
Let power consumed will be P. when operated on 110 V. Then
`P. = ((110)^(2))/(R)` …(2)
From (1) and (2), we have
`(P.)/(100)= ((110)/(220))^(2)`
or `P.= (1)/(4) xx 100`
or P.= 25W