An electric field in an e.m.wave is given by
`E=200 sin .(2pi)/lambda(ct-x)NC^-1`.
Find the energy contained in a cylinder of crossection `20 cm^2` and length 40 cm along the x-axis.

Explanation

Average energy density of the electromagnetic wave is
<`U_(av)> =(1)/(2)epsilonE_(0)^(2)=(1)/(2)xx8.55xx10^(-12)xx(50)^(2)=1.1xx10^(-8)Jm^(-3)`
Volume `10 (cm)^(2) xx 50 cm = 5 xx 10^(4) m^(3)`
U= volume xx energy density
=`5xx10^(4)xx1.1xx10^(8)=5.5xx10^(12)J`