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)Jm^(-3)`
B. `4.58xx10^(-6)Jm^(-3)`
C. `6.37xx10^(-9)Jm^(-3)`
D. `81.35xx10^(-12)Jm^(-3)`

Answer

B

Explanation

Total average energy density of electromagnetic wave is `gt u lt =(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)))(because B_("rms")=(E_("rms"))/(c))`
`=(1)/(2)epsilon_(0)E_("rms")^(2)+(1)/(2mu_(0))E_("rms")^(2)epsilon_(0)mu_(0)" "(because 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)`
`=(8.85xx10^(-12))xx(720)^(2)=4.58xx10^(-6)Jm^(-3)`