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Intensity of unpolarized light through two polarizers

  1. Apr 14, 2010 #1
    1. Unpolarized light with intensity 440 W/m2 passes first through a polarizing filter with its axis vertical, then through a polarizing filter with its axis 20.0 degrees from vertical.



    2. Malus's Law



    3. Ok, the intensity after going through the first polarizer should be 1/2 the original. This, after the second polarizer, I = 220*cos20) = 207 W/m2, which is incorrect.
     
  2. jcsd
  3. Apr 14, 2010 #2

    vela

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    The filter works by allowing only the parallel component of the electric field, E cos(theta), through. How are the electric field of the light and the intensity of the light related?
     
  4. Apr 14, 2010 #3
    I = P/A = 0.5c*epsilon_0*E^2

    Again, I don't see how to get I from P without knowing A.
     
  5. Apr 16, 2010 #4

    vela

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    You're getting too caught up in just brute force calculation when you should be focusing on how one quantity depends on another. You don't need to know P or A. Think ratios.
     
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