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

Options

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

Answer

D

Explanation

Here, the power rating of the electric bulb is P = 100W and the voltage rating is V = 220V
So, the resistance of the filament of the bulb is
`R = V^2/P`
`=((220)^2)/100`
`=484 Omega`

Now, the power consumed by the bulb when it is operated at 110 V is given by
`P. +(V.^2)/(R)`
` =((110)^2)/(484) = (110xx110)/484 =25 W`