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Homework Help: Total internal reflection

  1. Apr 16, 2014 #1
    1. Light traveling in air strikes a glass surface with n = 1.48. For what range of angles will total internal reflection occur?

    2. sinΘc = n2/n1

    3. I did this equation with air as n2 and glass as n1 and then got Θc=42.5°. After that I subtracted that from the normal (90°) and got 47.5°. Is this the right way to approach this? Just for the record this is for AP Physics B so no calculus should be used. Thank you!
  2. jcsd
  3. Apr 16, 2014 #2
    The question seems to have it backwards. It says " Light traveling in air strikes a glass". Shouldn't it be the other way around?

    Why are you subtracting if from 90°?
  4. Apr 17, 2014 #3
    I did that because from air to glass it makes the sin then not exist. So switched it and because I switched it I then subtracted the 90 degrees.
  5. Apr 17, 2014 #4
    Switching it changes the question (which may or may not be necessary. May be the original question has a typo. May be not).
    Subtracting from 90° makes no sense.
    Last edited: Apr 17, 2014
  6. Apr 17, 2014 #5
    So what should I do?
  7. Apr 17, 2014 #6


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    Go back to the original phrasing of the problem and the original equation,

    [tex] \sin \left( \theta_c \right) = \frac{n_2}{n_1} [/tex]
    Now the light starts off in the glass. So what's the original index of refraction, [itex] n_1 [/itex] or [itex] n_2 [/itex] ?
  8. Apr 18, 2014 #7
    Nothing. You're done. If you conclude there was no typo then, as you said, there is no sinθ, and if there is a typo than you already solved it in the OP, except that you shouldn't subtract your answer from 90°. There is no reason to do that.
  9. Apr 18, 2014 #8
    Ok. Cool then. Thanks a lot
  10. Apr 21, 2014 #9
    light refracts towards the normal when it travels from a rearer medium to a denser medium so how can we see a perfect image in the mirror it also consits of glass? please answer as fast as possible
  11. Apr 21, 2014 #10


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    What will happen when it again go out to air? (From a high dense to low dense medium?)
    Can you answer this question?
  12. Apr 21, 2014 #11
    The ray will bend away from the medium
  13. Apr 21, 2014 #12
    But sir there will be a difference as the ray will reflect back from where it is incident.
  14. Apr 21, 2014 #13
    Ooooooooh. Ok I got it now. Thanks for everything
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