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Homework Help: Thin Film Problem

  1. Oct 25, 2011 #1
    1. The problem statement, all variables and given/known data
    A thin film of alcohol (n=1.36) lies on a flat glass plate (n=1.51). When monochromatic light whose wavelength can be changed, is incident normally, the reflected light is minimum for λ=512 nm and a maximum for λ=640 nm. What is the thickness of the film?

    2. Relevant equations

    3. The attempt at a solution
    Let the thickness be t, then we have
    t/(512/1.36)=m+1/2 where m is an integer.
    t/(640/1.36)=n where n is an integer.
    Solving for t and setting the expressions equal, we get 376m+188=471n (using significant figures). I feel like I'm doing something wrong because of the resulting equation. Can someone help me? Thanks.
  2. jcsd
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