Plane-polarized electromagnetic waves

[twoscoops]

Homework Statement

Consider a plane-polarised electromagnetic wave in source-free vacuum, with magnetic field B = (1,1,0)BoCos(kz-wt), with Bo = 0.001 Tesla. Find
(1) the direction of propagation of the wave,
(2) average energy density carried by the wave, and
(3) the fraction of this energy which would pass through a perfect polariod sheet at normal incidence, if the angle between B and the transmission axis of the polariser is 30degrees.

Homework Equations

Uvpw = eoEo^2cos^2(kz-wt)
Bo=Eo/c
eo = 8.854x10^-12
Not really sure of any others

The Attempt at a Solution

(1)travelling in the +z direction
(2)Bo=Eo/c Eo= 10^5
<Uvpw> = eoEo^2x(average of cos^2) average cos^2 = 0.5
<Uvpw> = 0.5eoEo^2 = 0.398Jm-3

Im pretty sure the first two are right but I am stumped how to do part 3.
Thanks

 

[vela]

A polarizer let's the component of the electric field parallel to the transmission axis through; it blocks the perpendicular component.