The magnetic field in a plane electromagnetic wave is given by $B = 100\mu T \sin [(2 \times10^{15}s^{-1}) (t-x/c)]$. Calculate the average energy density corresponding to the electric field.

Question

$\begin {array} {1 1} (a)\;3.98 \times 10^{-3}J/m^3 & \quad (b)\;39.8 \times 10^{-3}J/m^3 \\ (c)\;39.8 \times 10^{-5}J/m^3 & \quad (d)\;3.98 \times 10^{-5}J/m^3 \end {array}$