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Light traveling through two mediums

  1. Dec 7, 2016 #1
    1. The problem statement, all variables and given/known data
    1234.PNG

    2. Relevant equations
    Thickness for destructive interference ( since we don't want any reflection)
    t = (wavelength) / (4 * index of refraction)
    v = wavelength * frequency
    c/n = v

    3. The attempt at a solution
    I figure since the wavelength will change going through the oil we need to calculate that first. We also know that frequency of the light wave won't change but its velocity and wave length will.

    So ... c / 525 nm will gives us constant frequency or f.

    Also will use speed of light divided by index of refraction of oil ... c/1.72 will give us the speed of light inside that medium which we will call V(oil)

    So then... V(oil) = wavelength * f.

    Then I took that wave length and divided it by 4* index of refraction of the fil.

    Is my reasoning and set u close or am I missing something conceptually?

    Thanks,
     
  2. jcsd
  3. Dec 7, 2016 #2
    The question wording is a little confusing, but it seems to be asking what the minimum thickness of the film can be that will allow the light to transmit through to the substrate so that it's not reflected, in which case you need to account for the relation between the n-values, the angle of refraction they cause, and the critical angle.
     
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