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Geometric Optics: Snell's Law calculation problem

  1. Mar 2, 2009 #1
    1. The problem statement, all variables and given/known data
    Calculate the angle of incidence for an angle of refraction of 10° for
    a) Diamond (2.42) to air

    θ2=Angle of refraction=10°
    n2=Index of refraction on refractive medium=1
    n1=index of refraction on incident medium=2.42

    2. Relevant equations

    3. The attempt at a solution
    The book's answer tells me the answer is 24.8°

    I rearranged the equation to find theta1 or the angle of incidence
    θ1=sin inverse(n2sinθ2/n1)

    I substituted the values and I got 4.1°

    Can someone help me? I can't figure out what I did wrong. Light is coming from a dense medium to a less dense medium (diamond to air) so where the incident ray originated from the dense medium which is n2. So confused..
  2. jcsd
  3. Mar 2, 2009 #2


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    Looks like the 10 degree angle is in the diamond, not in the air.
  4. Mar 2, 2009 #3
    Doesn't the light refract in the rare medium meaning the angle of refraction is in the air?
  5. Mar 2, 2009 #4
    Depends what the question is...

    in the question, is light travelling from air to diamond or from diamond to air?

    if latter case is correct then your set up seems to be right...

    if the first case is correct then set up must be changed
  6. Mar 3, 2009 #5


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    Okay, reading things more carefully, it looks like whoever wrote this question messed up.

    The question statement says "diamond to air", suggesting diamond is the incident medium. The refracted angle (10°) would then be in air.

    But the given answer, 24.8°, implies they meant things the other way around.

    4.1° is correct, given what the question asked.
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