In a plane e.m. wave, the electric field varies with time having an amplitude `1Vm^-1`. The frequency of wave is `0.5xx10^(15) Hz`. The wave is propagating along Z-axis. What is the average energy density of (i) electric field (ii) magnetic field (iii) total average energy density (iv) what is the amplitude of magnetic field?

Options

A. The average energy density of electric field is `2.21 xx 10 ^(-12)J m ^(-3).`
B. The average energy density of total field is `4.42 xx 10 ^(-12) J m ^(-3).`
C. The average enerfy density of total field is `6.91 xx 10 ^(-12)J m ^(-3).`
D. The amplitude of magnetic field is `3.33 xx 10 ^(-9) T.`

Answer

A, B, D

Explanation

`u _(E) =1/4 epsi _(0) E _(0) ^(2) =1/4 xx 8.85 xx 10 ^(-12) xx 1 ^(2) = 2.21 xx 10 ^(-12) J m ^(-3)`
`u _(B) = u _(E) =2.21 xx 10 ^(-12) J m ^(-3)`
` u _(av) = u _(E) + u _(B) = 2 xx 2.21 xx 10 ^(-12) = 4.42 xx 10 ^(-12) J m ^(-3)`
`B_(0) = (E _(0))/( c) = (1)/( 3 xx 10 ^(8)) = 3.33 xx 10 ^(-9) T`