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Homework Help: Total internal reflection

  1. Apr 18, 2010 #1
    1. The problem statement, all variables and given/known data

    What is the maximum value of θ1 that would cause total internal reflection to occur? N1 = 1.3, n2 = 1.6 (picture attached)

    2. Relevant equations

    Critical angle = sin^-1(n1/n2)

    3. The attempt at a solution

    I figured the critical angle to be 54.3. That means that theta1 has to be less than 35.7 degrees in order for total internal reflection to occur, correct? However, the answer that I am supposed to get is 22.6 degrees.

    I am interested in seeing how this problem works out, but I'm also a bit shaky on the critical angle concept. Thanks for the help!
     
  2. jcsd
  3. Apr 18, 2010 #2

    Doc Al

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    Staff: Mentor

    Post the diagram.
     
  4. Apr 18, 2010 #3
    Oops, it's attached now.
     

    Attached Files:

  5. Apr 18, 2010 #4

    Doc Al

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    Staff: Mentor

    The diagram shows three layers. What are their indices? Where is the total internal reflection supposed to take place?
     
  6. Apr 18, 2010 #5
    Only the top two layers are used in this problem. The ray is coming from layer 1 and reflecting off layer 2.

    I posted the indices in my first message.
     
  7. Apr 18, 2010 #6

    Doc Al

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    But total internal reflection takes place when light reflects off a layer with a lower index of refraction.
     
  8. Apr 18, 2010 #7
    N3 is 1.2, if that helps. In this case, then, I would assume that the ray bounces off the N2/N3 border. Sorry for the confusion! You can see that I don't really have a grasp on the topic :blushing:
     
  9. Apr 18, 2010 #8

    Doc Al

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    Staff: Mentor

    That makes more sense. So give it a second try. First find θ2, then use it to find θ1.
     
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