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Homework Help: 3 pieces of Polaroid sheet (light intensity)

  1. Apr 7, 2009 #1
    1. The problem statement, all variables and given/known data
    Unpolarized light of intensity I0 passes through two pieces of Polaroid sheet. The second piece is rotated so that the intensity of the transmitted light goes to zero. A
    third piece of Polaroid is inserted between the two pieces. Calculate the intensity as
    a function of the angle Θ that the axis of the middle piece makes with the axis of the
    first piece. By calculating the derivative of the intensity as a function of angle, find
    the angle that maximizes the intensity for this three-sheet arrangement.

    2. Relevant equations

    I0 = E2

    (1/2)I0 = I1 (after 1st sheet

    then, I = E2cos2Θ

    dsinΘ = mλ

    3. The attempt at a solution

    After passing the first sheet, I = (1/2) I0
    Then, (1/2)I0 = E2cos2Θ

    after that i dont know what to do...
  2. jcsd
  3. Apr 8, 2009 #2


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    Homework Helper

    Two Polaroid are in crossed position. When the third Polaroid is rotated through an angle theta Intensity through it is I = E^2cos^2(theta).Axis of the second Polaroid makes an angle (90 - theta) with the axis of the middle sheet. Hence intensity of the light from the second sheet I' = E^2cos^2(theta)*cos^2(90 - theta)
    or I' = E^2cos^2(theta)*sin^2( theta)
    Further simplify it. Differentiate with respect to theta and equate it to zero to get the angle for maximum and minimum intensity.
  4. Apr 8, 2009 #3
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