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Homework Help: Optics Question

  1. Jan 22, 2008 #1
    1. The problem statement, all variables and given/known data

    A)Two flat slides of glass are separated at one edge by a thin wire. The top surface of the upper slide and the bottom surface of the lower slide have special coatings on them so that they reflect no light. The system is illuminated with light of wavelength 418 nm. Looking down from above you see 40 interference minima. What is the diameter of the wire? Assume that the last minima occurs at the right edge where the wire is placed.

    B) Now by submerging the system in a certain liquid we find that the number of interference minima has increased to 49. What is the index of refraction of the liquid?

    2. Relevant equations

    For minima: d*sin(theta) = (n)*(lambda)

    3. The attempt at a solution

    I don't even know where to begin with this one...
    I would guess that you find the phase change and then can calculate the space between minima and add them to find the diameter for part A. The only issue is there doesn't seem to be enough information to do this! Help please!
  2. jcsd
  3. Jan 23, 2008 #2


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    Think about the spacing of the slides at the opposite edge... what is the form of the spacing across the slide? So what is the condition for each minima? (hint: your equation is incomplete). Once you understand that it should be fairly straightforward.
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