Question

An electric bulb is rated 220V and 100W. when it is operated on 110V, what will be the power consumed?

Why we are using P = V2/R formula while solving and not using P= VI formula

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Answer 1

Answer:

Potential difference across bulb = 220V

Power of bulb = 100 W

=>. V^2/R = 100

220 x 220 / R = 100

R = 22 x 22

R = 484

Therefore, the when operated with 110V bulb,

The power = 110 x 110 / 484

= 25 W

Explanation:

We can't use P= VI because electric current changes with potential difference but resistance doesn't