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The resistance of the filament of a lamp...

The resistance of the filament of a lamp increases with the increase in temperature. A lamp rated `100 W` and `220 V` is connected across `220 V` power supply. If the voltage drops by `10%`, then the power of the lamp will be

A

90 W

B

81 W

C

Between 90W and 100 W

D

Between 81 W and 90 W

Text Solution

Verified by Experts

The correct Answer is:
D
Initially `P = V^(2)/R rArr 100 = (220)^(2)/R`
When voltage drops,
`P = (220 xx 0.9)^(2)/R^(.) = 81 W` Here `R. lt R`
`therefore P gt (220 xx 0.9)^(2)//R = 81 W`
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