Question

If the electric current in a lamp decreases by $5\%,$ then the power output decreases by

• A. 2.5 $\%$
• B. 10 $\%$
• C. 5 $\%$
• D. 20 $\%$

Answer 1

Answer: (B)

Power of lamp
$P=i^{2}R$
or $\frac{dP}{P}=2\frac{\Delta i}{i}=2\times 5\%(\because \frac{\Delta i}{i}=5\%)$
$ =10 \% \$ decrease