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Homework Help: AS Physics - Polarisation Problems.

  1. Dec 22, 2011 #1
    Hey guys.

    I need some help on understand a few concepts and have some questions

    1. How is light polarised when it is reflected?

    2. Are there different amounts of light vibrating in each direction, or is it equal?

    3. From my revision guide:

    "If you direct a beam of unpolarised light at a reflective surface then view the reflected ray through a polarising filter, the intensity of the light leaving the filter changes with the orientation of the filter.

    The intensity changes because light is partially polarised when it is reflected.

    This effect is used to remove unwanted reflections in photography, and in Polaroid sunglasses to remove glare."

    - But wouldn't the light intensity leaving the filter change if it wasn't reflected off a surface, and just fired directly through a polarising filter? (Providing that each direction of vibration contains different amounts of light intensity)

    - How is the intensity changing due to the light being partially polarised when it is reflected? I thought that it might be because there are different amounts of vibrations and/or light intensity in each direction?

    Thank you for taking the time to read this and reply. It's much appreciated.
  2. jcsd
  3. Dec 23, 2011 #2


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    Welcome to Physics Forums.
    The two polarizations have different reflectivities (except at normal incidence), so a reflected beam will have different amounts of power in the two polarization directions.

    See above.

    Unpolarized light contains the same amount of each polarization. So if "each direction of vibration contains different amounts of light intensity", then it is partially polarized, and not unpolarized.
    As I said earlier, the two polarizations have different reflectivities, except at normal incidence.
    You're welcome :smile:

    EDIT: For more info, you can google "fresnel coefficients".
    Last edited: Dec 23, 2011
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