Question

A point source of $100 \,W$ emits light with $5 \%$ efficiency At a distance of $5\, m$ from the source, the intensity produced by the electric field component is:

• A. $\frac{1}{40 \pi} \frac{W}{m^2}$
• B. $\frac{1}{10 \pi} \frac{W}{m^2}$
• C. $\frac{1}{20 \pi} \frac{W}{m^2}$
• D. $\frac{1}{2 \pi} \frac{W}{m^2}$

Answer 1

Answer: (A)

$\frac{1}{40 \pi} \frac{W}{m^2}$

Answer 2

The correct option is(A): $\frac{1}{40 \pi} \frac{W}{m^2}$

$I_{EF}​=\frac{1}{2}​×\frac{5}{4π×5^2}​$

$=\frac{1}{40π}1​W/m^2$