Current Electricity Ques 80
80. If voltage across a bulb rated 220 Volt- 100 Watt drops by $2.5 \%$ of its rated value, the percentage of the rated value by which the power would decrease is :
[2012]
(a) $20 \%$
(b) $2.5 \%$
(c) $5 \%$
(d) $10 \%$
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Answer:
Correct Answer: 80.(c)
Solution:
- (c) Resistance of bulb is constant
$P=\frac{V^{2}}{R} \Rightarrow \frac{D p}{p}=\frac{2 D V}{V}+\frac{D R}{R}$
$\frac{D p}{p}=2 \times 2.5+0=5 \%$
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