Question

An observer is $4m$ away from a CFL (point source) having $270$ $watt$ power. Find $E_{rms}$ at the observer?

• A. $22.5$ $N/C$
• B. $45$ $N/C$
• C. $22.552$ $N/C$
• D. $36$ $N/C$

Answer 1

The correct option is A $22.5$ $N/C$

$I={ϵ}_0{E}_{rms}^2.C$
$E_{rms}=\sqrt{\frac{I}{C{ϵ}_0}}$
$=\sqrt{\frac{P}{4\pi r^2.C{ϵ}_0}}=\sqrt{K\frac{P}{C{r}^2}}$
$=\sqrt{\frac{9\times {10}^9\times 270}{3\times {10}^8\times 16}}=\sqrt{\frac{9\times 27\times 100}{3\times 16}}=\sqrt{\frac{9\times 9\times 100}{16}}$
$E_{rms}=\frac{9}{4}\times 10=\frac{90}{4}=22.5$$N/C$