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Homework Help: Regarding Total Internal Reflection

  1. Oct 16, 2007 #1
    Regarding "Total Internal Reflection"

    Hi, and thanks in advance for viewing this post.

    I'd like to type out the question first;

    Q: Consider the optical interface between crown glass and ethanol.
    a) Under what conditions would total internal reflection be possible at this interface?
    Illustrate your answer with a light-ray diagram.

    b) White light travels from crown glass into ethanol. If the angle of incidence in crown
    glass is 60.00 degrees (not sure how to insert degree sign), what is the angular spread
    between the red and violet parts of the visible spectrum in the ethanol? Illustrate your
    answer with a light-ray diagram.

    c) Light travels from ethanol into crown glass. What is the Brewster angle in this
    situation? Illustrate your answer with a light-ray diagram. What is the significance of
    this angle of incidence?

    Ok, so I have completed question a) and b). (Still working on c).
    Any correction/advice would be greatly appreciated! Thanks again!

    a) In order for the total internal reflection to occur, the light must enter from higher
    index of refraction to a lower index of refraction, which in this case, Crown glass -->
    Ethanol. In addition, the incident angle must be greater than the critical angle, which
    is 63 degrees.
    Crown glass = 1.52 > Ethanol = 1.36
    Sinθc = (1.36)(1.00) / 1.52
    θc = 63 degrees.

    http://img146.imageshack.us/img146/5690/spa0202ux3.th.jpg [Broken]

    b) Calculation
    θi = 60 degrees
    n1 = 1.520 (for red light in crown glass)
    n2 = 1.376 (for violet light in crown glass)
    nR = 1.36 = Ethanol

    For red light;
    (will omit calculation due to complication of work on this thread lol)
    sinθR = 75 degrees

    For violet light;
    sinθR = 88 degrees

    θdisplacement = θR(violet) - θR(red)
    Therefore, θdisplacement = 88 - 75 = 13 degrees.

    http://img513.imageshack.us/img513/3772/spa0201aj8.th.jpg [Broken]

    I apologize for the work not being neat T_T

    I'm still working on the question C so i will add to the post when its complete hehe

    Thank you very much!! again!!!
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Oct 16, 2007 #2

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    There is no problem with this; I haven't checked the calculated numbers, but your logic is correct and if you can work that abacus correctly, I'll assume the numbers are right.

    C is the easiest part. Look under polarization.
  4. Oct 16, 2007 #3
    Thank you Chi Meson, I hope my works get perfect lol :\
    and yep, for the part c, I've wrote down how the incident, or the Brewster angle
    indicate that the reflected light is completely polarized parallel to the interface.

    Thanks again!
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