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Homework Help: Plane-polarized electromagnetic waves

  1. Aug 7, 2010 #1
    1. The problem statement, all variables and given/known data

    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.

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

    3. 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 im stumped how to do part 3.
    Thanks
     
  2. jcsd
  3. Aug 8, 2010 #2

    vela

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