Question

The peak electric field produced by the radiation coming from the $8W$ bulb at a distance of $10m$ is $\frac{x}{10}\sqrt{\frac{\mu _{0} C}{\pi }}\frac{V}{m}$ . The efficiency of the bulb is $10\%$ and it is a point source. The value of $x$ is _____.

Answer 1

$I=\frac{1}{2}C\in _{0}E_{0}^{2}$
$\frac{8}{4 \pi \times 10^{2}}=\frac{1}{2}\times c\times \frac{1}{\mu _{0} C^{2}}\times E_{0}^{2}$
$E_{0}=\frac{2}{10}\sqrt{\frac{\mu _{0} C}{\pi }}$
$\Rightarrow x=2$