Question

what is the energy density of electric field at a distance of 5m from a point source of EMwave if the electric field strength at that point be 100v/m

Answer 1

Electric field $\left(E\right)=100\frac{V}{m}$

Energy density $\left(U_D\right)=\frac{1}{2}{\epsilon }_0{E}_{max}^2$

$=\frac{1}{2}\times (8.85\times {10}^{-12})\times {\left(100\right)}^2$

$=4.425\times {10}^{-8}J{m}^{-2}$