The electric field of a plane electromagnetic wave varies with time of amplitude `2Vm^-1` propagating along z-axis. The average energy density of the magentic field is (in `Jm^-3`)

Options

A. `13,29xx10^(-12)`
B. `8.86xx10^(-12)`
C. `17.72xx10^(-12)`
D. `4.43xx10^(-12)`

Answer

B

Explanation

Amplitude of electric field and magnetic field are related by the relation `(E_(0))/(B_(0))=c`
Average energy density of the magnetic field is `u_(B)=(1)/(4)(B_(0)^(2))/(mu_(0))`
`=(1)/(4)(E_(0)^(2))/(mu_(0)c^(3))" "(because B_(0)=(E_(0))/(c))`
`=(1)/(4)epsilon_(0)E_(0)^(2)" "(because c=(1)/(sqrt(mu_(0)epsilon_(0))))`
`=(1)/(4)xx8.854xx10^(-12)xx(2)^(2)~~8.86xx10^(-12)Jm^(-3)`