Question

The average value of electric energy density in an electromagnetic wave is ( $E_{0}$ is peak value)

• A. $\frac{1}{2} \varepsilon_{0} E_{0}^{2}$
• B. $\frac{E_{0}^{2}}{2 \varepsilon_{0}}$
• C. $\varepsilon_{0} E_{0}^{2}$
• D. $\frac{1}{4} \varepsilon_{0} E_{0}^{2}$

Answer 1

Answer: (D)

Electric energy density
$ u_{e}=\frac{1}{2} \varepsilon_{0} E_{ rms }^{2} $
$E_{\text{rms }} =\frac{E_{0}}{\sqrt{2}} $
$\therefore u_{e}=\frac{1}{4} \varepsilon_{0} E_{0}^{2}$