# A $60W$ monochromatic point source radiating equally in all directions in vacuum is being monitored at a distance of $2m$. Determine the amplitude if the electric field.

$\begin {array} {1 1} (a)\;30.06 \: N/C & \quad (b)\;3.006\: N/C \\ (c)\;300.06\: N/C & \quad (d)\;0.3006\: N/C \end {array}$

Intensity, $I = \large\frac{P}{4 \pi r^2}$
$= \large\frac{60}{(4 \times 3.14 \times 4)} $$= 1.194 W/m^2 E_o = \sqrt{ \bigg( \large\frac{2I}{\in_oc} \bigg) } = \sqrt{ \bigg[\large\frac{2 \times 1.194}{(8.85 \times 10^{-12} \times 3 \times 10^8)} \bigg]}$$ = 30.06 N/C$
Ans : (a)