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Light and Absorptive polarizers

  1. Mar 19, 2008 #1
    1. The problem statement, all variables and given/known data

    I was thinking about the 3 polarizers experiment where you have them angled 45 degree to each other and the first and third are perpendicular.

    With 2 polarizer angles 90 degree to each other, no light passes through.
    But with a third one inserted between them at a angle of 45 to the 1st and 3rd, light can pass through at a lower intensity.

    I like to ask why?

    2. Relevant equations

    none.

    3. The attempt at a solution

    With 2 polarizer angles 90 degree to each other, no light passes through.
    But with a third one inserted between them at a angle of 45 to the 1st and 3rd, light can pass through at a lower intensity.

    I'm pondering on the why this happens. I've read a little bit of how the polarizers work. The electromagnetic waves must be perpendicular to the length of the metal grating so that it can pass through with a little loss of energy. Is this correct?

    Secondly would diffraction have any part in the explanation?
    Because I'm thinking the light in the one direction is diffracted. With the 2 polarizers, the interference pattern is absorbed by the 2nd polarizers, since all the light is parallel to the metal grating. But when a new polarizer is inserted between them, the light is firstly diffracted in a new direction through the 2nd polarizer which can pass through the 3rd lens?

    This makes me wonder about another question.
    Was the double slit experiment performed with monochromatic polarized light? Does it make a differences?

    Thanks for your help
     
  2. jcsd
  3. Mar 19, 2008 #2

    Chi Meson

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    Science Advisor
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    No, that is not it.
    none, whatsoever.

    Polarization and diffraction are completely different phenomena.

    Polarization has to do with the transverse nature of light waves. Photons are an oscillation of electric and magnetic fields. THe direction of this oscillation is perpendicular to the direction in which the photon travels. Normal light is composed of many photons oscillating in random planes (up-down side-to-side, cross-ways). When transmitting through polarizing material, those photons oscillating in a certain direction will be absorbed by the material.

    Those photons that oscillate cross-ways will have a portion of their energy absorbed such that all the light that transmits will be oscillating in one plane only. If the middle polarizer is put in at 45 degrees, then a portion of the polarized light will be transmitted such that the transmitted light is now in a 45 degree plane. The third filter is 45 degrees (not 90) to the second, so a portion of that light will be transmitted.
     
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