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Homework Help: 3 perfect polarizing films

  1. Nov 11, 2005 #1
    If you have 3 perfect polarizing films and you place them on top of the other, with each successive film oriented +45 degrees from the one before it (first and last oriented perpendicular to each other and middle polarizer at 45 degrees between them). If one shines a light on this polarizer stack with an intensity of 1 watt, what is the intensity of the light on the other side of the three polarizer stack?

    Now when I tried to figure this out I assume that the light is collimated and that the films are perfect polarizer. But I got stuck on the actually equation... Anyone out there knows how to solve this?
  2. jcsd
  3. Nov 12, 2005 #2


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    Perhaps the Law of Malus applies.

    For each polarizer - Itrans = Io cos2[itex]\theta[/itex], where [itex]\theta[/itex] is the angle of between axis of polarizer and some reference.

    The question is what is the transmission of light through the first polarizer.

    Edit: See http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polcross.html

    for discussion of crossed polarizers and Law of Malus.
    Last edited: Nov 12, 2005
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