In an electromagnetic wave, the amplitude of electric field is 1 V/m. the freque

Question

In an electromagnetic wave, the amplitude of electric field is 1 V/m. the frequency of wave is

5 \times 10^{14}

Hz. The wave is propagating along z-axis. The average energy density of electric field, in

J o u l e m^{3}

, will be

Options:

A . 1.1× 10−11

B . 2.2× 10−12

C . 3.3× 10−13

D . 4.4× 10−14

Answer: Option B
:
B
Average energy density of electric field is given by

u_{e} = \frac{1}{2} ϵ_{0} E^{2} = \frac{1}{2} ϵ_{0} {(\frac{E_{0}}{\sqrt{2}})}^{2} = \frac{1}{4} ϵ_{0} E_{0}^{2}

= \frac{1}{4} \times 8.85 \times 10^{- 12} (1)^{2} = 2.2 \times 10^{- 12} J / m^{3} .

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