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Length of optical path

  1. Aug 25, 2014 #1
    1. The problem statement, all variables and given/known data

    for diagram 2 , i just cant understand why S1P -t + ut (upper ray ) is longer than the lower light ray (S2P) , ? if I take S2P minus ( S1P -t + ut ) , then i would get mt t (thickness ) is negative , which is indeed wrong! so it has shown that optical path of the upper ray is longer than the optical path of lower ray ....

    2. Relevant equations

    3. The attempt at a solution

    Attached Files:

  2. jcsd
  3. Aug 25, 2014 #2


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    S1P - t + ut > S2P if u>1, as S2P=S1P based on the upper diagram. I guess u is your refractive index? Regular materials have a refractive index larger than 1, so the upper path is longer.
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