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If voltage across a bulb rated $220 \mathrm{~V}-100 \mathrm{~W}$ drops by $2.5 \%$ of its rated value, the percentage of the rated value by which the power would decrease is
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Verified Answer
The correct answer is:
$5 \%$
Power $P=\frac{V^2}{R}$
For small variation
$\begin{aligned}
\frac{\Delta P}{P} \times 100 \% & =\frac{2 \times \Delta V}{V} \times 100 \% \\
& =2 \times 2.5=5 \%
\end{aligned}$
Therefore, power would decrease by $5 \%$.
For small variation
$\begin{aligned}
\frac{\Delta P}{P} \times 100 \% & =\frac{2 \times \Delta V}{V} \times 100 \% \\
& =2 \times 2.5=5 \%
\end{aligned}$
Therefore, power would decrease by $5 \%$.
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