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Homework Help: Index of when refraction/optics question

  1. Jun 23, 2016 #1
    The question
    A microscope is focused on a black dot. When a 1.20 cm -thick piece of plastic is placed over the dot, the microscope objective has to be raised 0.380 cm to bring the dot back into focus.

    What is the index of refraction of the plastic

    Relevant equations/ideas

    Trying to solve
    I know I must use triangles to figure out the angles needed for Snells law, but have more unknown variables than equations to relate them so I dont know how to solve for them
    Last edited: Jun 23, 2016
  2. jcsd
  3. Jun 23, 2016 #2


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    Homework Helper
    Gold Member

    Have you come across real and apparent depth? For example, when you look into a pool of water, it appears shallower than it really is, due to refraction.

    Also, you could pick an arbitrary angle and do the calculation for that. Edit: And I'd always start with a diagram (or several.)
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