The electric field in $\mathrm{NC}^{-1}$ of an electromagnetic wave is $\mathrm{E}=36 \sqrt{\pi}…
The electric field in $\mathrm{NC}^{-1}$ of an electromagnetic wave is $\mathrm{E}=36 \sqrt{\pi} \operatorname{Sin}(\omega \mathrm{t}-\mathrm{kx})$. The average energy density of the electromagnetic wave due to the electric field is $\left(\frac{1}{4 \pi \varepsilon_0}=9 \times 10^9 \mathrm{Nm}^2 \mathrm{C}^{-2}\right)$
$36 \times 10^{-9} \mathrm{Jm}^{-3}$
$18 \times 10^{-9} \mathrm{Jm}^{-3}$
$36 \times 10^{-7} \mathrm{Jm}^{-3}$
$18 \times 10^{-7} \mathrm{Jm}^{-3}$
Solution
The average encrgy density of the electromagnetic wave is given by
$\begin{aligned}
& \mathrm{U}_{\mathrm{av}}=\frac{1}{2} \epsilon_0 \mathrm{E}^2 \\
& =\frac{1}{2} \times 8.86 \times 10^{-12} \times(36)^2 \pi=18 \times 10^{-9} \mathrm{~J} / \mathrm{m}^3
\end{aligned}$