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Question

Physics Question on Electromagnetic waves

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

4.58×10−6 J/m34.58 \times10^{-6} \,J/m^{3}

B

6.37×10−9 J/m36.37 \times10^{-9} \,J/m^{3}

C

81.35×10−12 J/m381.35 \times10^{-12} \,J/m^{3}

D

3.3×10−3 J/m33.3 \times10^{-3} \,J/m^{3}

Answer

4.58×10−6 J/m34.58 \times10^{-6} \,J/m^{3}

Explanation

Solution

Total average energy =ε0Erms2=\varepsilon_{0}E^{2}_{rms} =8.85×10−12×(720)2=8.85 \times10^{-12} \times\left(720\right)^{2} =4.58×10−6 j/m3=4.58\times10^{-6}\,j/m^{3}