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)

10 $\%$

Answer 2

Power of lamp
\hspace15mm P=i^2R
or \hspace15mm \frac {dP}{P}=2 \frac {? i}{i}= 2 \times 5 \% \hspace5mm \bigg (\because \frac {? i}{i}=5 \% \bigg )
\hspace15mm =10 \% \ decrease