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An electric bulb is marked \mathrm{100 W, 230 V.} If the supply voltage drops to \mathrm{115 V}, what is the heat and light energy produced by the bulb in \mathrm{20 \: min}?

Option: 1

20,000\mathrm{J}


Option: 2

25,000\mathrm{J}


Option: 3

30,000\mathrm{J}


Option: 4

35,000\mathrm{J}


Answers (1)

best_answer

Here, \mathrm{P = 100 W; V = 230 V}

Let R be resistance of the filament of the bulb.

Now,electric power ,\mathrm{P =VI=\frac{V^{2}}{R}}

Therefore,\mathrm{R}=\frac{\mathrm{V}^2}{\mathrm{P}}=\frac{(230)^2}{100}=529 \Omega

When the voltage drops to 115 \mathrm{~V}, heat and light energy produced by the bulb in 20 \mathrm{~min} is given by

\mathrm{V}=\mathrm{VIt}=\frac{\mathrm{V}^2}{\mathrm{R}} \mathrm{t}=\frac{(115)^2}{529} \times 20 \times 60=30,000 \mathrm{~J}

Hence option 3 is correct

Posted by

himanshu.meshram

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