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Total Internal Reflection / Reflection. What's the answer

  1. Nov 20, 2016 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations


    3. The attempt at a solution
    https://scontent-kul1-1.xx.fbcdn.net/v/t35.0-12/15146781_1334186669946177_363846788_o.jpg?oh=b75be99f63eba2e70db5e0287581076b&oe=583538C2
    The answer given by the book is " Reflection ". But why isn't it Total Internal Reflection ?
     
  2. jcsd
  3. Nov 21, 2016 #2

    blue_leaf77

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    Total internal reflection occurs only at specific range of angle of incidence. Moreover, is "total internal reflection" among the choices?
     
  4. Nov 21, 2016 #3
    The choices are
    A. Reflection
    B. Refraction
    C. Diffraction
    D. Total Internal Reflection.
     
  5. Nov 21, 2016 #4

    haruspex

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    The diagram is a bit off. You would not see the water surface as a line, and the reflection would not look exactly like the directly viewed animal.
    The head is so near the surface it would certainly be total internal reflection, and the rest of the reflection is shown as being as strong, suggesting it is all TIR.
     
  6. Nov 21, 2016 #5

    jbriggs444

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    It is difficult to know how much of the depiction to take as realistic and how much to take as illustrative. For instance, the entire reflection is less "strong" than the directly viewed image. That could be taken as a meaningful tidbit of information or it could be taken as artistic license to more clearly delineate between directly viewed image and reflection. As @haruspex points out, the head is depicted as strongly as the rest, so one is forced to a conclusion that it is artistic license.

    The image is quite symmetric about the horizontal axis. There is no asymmetry which would suggest an eye position much below the water line. That would support the idea that this is TIR. However, there are no good distance cues, so we cannot accurately judge the viewing angle for the bottom of the lake or river bed, the bottom-most portion of which is not even present in the reflected image.

    For me it is the lack of reliable information about the viewing angle for the extreme top of the image which leads to the conclusion that "reflection" is the desired answer.
     
  7. Nov 21, 2016 #6

    NascentOxygen

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    The throat and belly are facing away from the interface yet appear in the image. It is difficult to see how a simple reflection could reveal the creature's underside here.
     
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