Question

Choose the correct answer from the alternatives given.
The rms value of the electric field of the light coming from the Sun is 720 N/C. The average total energy density of the electromagnetic wave is

• A. $3.3\times {10}^{-3}J/m^3$
• B. $4.58\times {10}^{-6}J/m^3$
• C. $6.37\times {10}^{-9}J/m^3$
• D. $81.35\times {10}^{-12}J/m^3$

Answer 1

The correct option is B $4.58\times {10}^{-6}J/m^3$

Given: The RMS value of the electric field of light is $720N/C$.

Energy density of electromagnetic wave is given by:

$E={ϵ}_0{E}_{rms}^2$

$\Rightarrow {ϵ}_0\times (720{)}^2$

$\approx 4.58\times {10}^{-6}J/m^3$

Option $\left(B\right)$ is corret.