Question

If the current in an electric bulb decreases by $0.5$%, the power in the bulb decreases by approximately

• A. $1$%
• B. $2$%
• C. $0.5$%
• D. $0.25$%

Answer 1

Answer: (A)

$1$%

Current decrease by $5\%$ means $\frac{dI}{I}=0.5$%

Power, $P=I^{2}R\Rightarrow dP=R2IdI$

Power decrease $=\frac{dP}{P}=\frac{R2IdI}{I^{2}R}=\frac{2dI}{I}=2\times 0.5\%=1$%