A red LED emits light at 0.1W uniformly around it. The amplitude of the electric field of the light at a distance of 1m from the diode is

We know that Intensity at r from the source is given as,

$I=\frac{P}{4\pi r^2}\to \left(1\right)$

And We know that, $I=\left(\frac{1}{2}{\in }_0{E_0}^2\right)C\to \left(2\right)$

From equation (1) & (2) , we get

$\frac{P}{4\pi r^2}=\frac{1}{2}{\in }_0{E_0}^2\times C$

${E_0}^2=\frac{2P}{4\pi r^2{\in }_{0}C}=\frac{2\times 0.1\times 9\times {10}^9}{1\times 3\times {10}^8}$

$$\begin{gathered} {E_0}^2=6 \\ \Rightarrow E_0=\sqrt{6}=2.45 V/m \end{gathered}$$