First slide

Electrical power

Question

If voltage across a bulb rated 220 V and 100 W drops by 2.5% of its rated value, by which the power would decrease is,

Moderate

A

5%
B

10%
C

20%
D

2.5%

Solution

Given $(\frac{Δ V}{V} \times 100) % = 2.5 %$
$P = \frac{V^{2}}{R} error in R = 0$
$(\frac{ΔP}{P} \times 100) % = 2 (\frac{ΔV}{V} \times 100) %$
$= 2 \times 2.5 % = 5 %$

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