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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:

1. 20%
2. 2.5%
3. 5%
4. 10%

Correct answer: 5%

Solution

The power of a bulb is proportional to the square of the voltage (P ∝ V²). A 2.5% drop in voltage corresponds to a decrease in power by (2 × 2.5%) = 5%.

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