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

Question

If voltage across a bulb rated 220V and 100W drops by 2.5 % of its rated value, by which the power would decrease is, (A) 5 % (B) 10 % (C) 20 % (D) 2.5 %

Tardigrade Admin · Accepted Answer

Given ((Δ V/V) × 100) %=2.5 % P=(V2/R) error in R=0 ((Δ P/P) × 100) % =2((Δ V/V) × 100) % =2× 2.5 %=5 %

Q. 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,

$5%$

$10%$

$20%$

$2.5%$

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

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

5%

10%

20%

2.5%