The rms value of the electric field of the light from the sun is `720 N//C` The total energy density of the electromagnetic wave is

Options

A. `3.3xx10^(-3)"J m"^(-3)`
B. `4.58xx10^(-6)"J m"^(-3)`
C. `6.37xx10^(-9)"J m"^(-3)`
D. `81.35xx10^(-12)"J m"^(-3)`.

Answer

B

Explanation

Total average energy density of electromagnetic wave is
`U_(av) = (1)/(2) epsilon_(0) E_("rms")^(2) +(1)/(2mu_(0))B_(rms)^(2)`
`= (1)/(2) epsilon_(0)E_(rms)^(2)+(1)/(2mu_(0)) ((E_(rms)^(2))/(c^(2))) ( :' B_(rms) = (E_(rms))/(c))`
`= (1)/(2) epsilon_(0) E_(rms)^(2) +(1)/(2mu_(0)) E_(rms)^(2) epsilon_(0) mu_(0) ( :' c = (1)/(sqrt(mu_(0)epsilon_(0))))`
`= (1)/(2) epsilon_(0)E_(rms)^(2) +(1)/(2) epsilon_(0)E_(rms)^(2) = epsilon_(0)E_(rms)^(2)`
`= 8.85 xx 10^(-12) xx(720)^(2) = 4.58 xx 10^(-6) J m^(-3)`