1.

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

Answer»

100W
75W
50W
25W

Solution :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 bulbwhen it is OPERATED at 110 V is given by
`P. +(V.^2)/(R)`
` =((110)^2)/(484) = (110xx110)/484 =25 W`


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