Current Electricity - Result Question 66
71. 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: 71. (c)
Solution:
- (c) Resistance of bulb is constant
$P=\frac{V^{2}}{R} \Rightarrow \frac{D p}{p}=\frac{2 D V}{V}+\frac{D R}{R}$
$\frac{D p}{p}=2 \times 2.5+0=5 %$
