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Geometrical problem related to thin film interference

  1. Aug 1, 2011 #1
    Look at the picture below, I have to prove that the optical path length difference is

    [itex] \Delta=n(BC+CD)-BE=2nd\cos(r)[/itex]

    [PLAIN]http://img200.imageshack.us/img200/2271/schermata082455775alle1.th.png [Broken]

    The problem is just how to get [itex]2nd\cos(r)[/itex]

    I actually don't have any idea :\

    I have tried to work with trigonometry but no luck yet...

    (I am posting it here because it's not related to course work, i am just trying to understand how it works when we don't have perpendicular incidence)
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Aug 1, 2011 #2
    Sorry, here we go with the pic:

    [PLAIN]http://img193.imageshack.us/img193/2271/schermata082455775alle1.png [Broken]
    Last edited by a moderator: May 5, 2017
  4. Aug 1, 2011 #3
  5. Aug 2, 2011 #4
    Thanks a lot :)
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