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Question
An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be ______.
Options
100 W
75 W
50 W
25 W
Solution
An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be 25 W.
Explanation:
Resistance of the bulb
∴ P = `"V"^2/"R"`
R = `"V"^2/"P"`
= `(220 "V"^2)/100`
= 484 Ω
Then, Power consumed at 110 V
P' = `("V'")^2/"R"`
= `(110 "V"^2)/484`
= 25 W
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