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Snell's Law Question

  1. Apr 4, 2016 #1
    1. The problem statement, all variables and given/known data
    A ray of light is incident on a flat surface of a block of gallium phosphide that is surrounded by water. The angle of refraction is 8.0°. Find the angle of reflection.

    2. Relevant equations
    n1 sin(theta1) = n2 sin(theta2)

    3. The attempt at a solution
    I keep finding different values for the index of refraction of gallium phosphide... 3.20 (which was wrong), 3.8 (also wrong)... can anyone verify what the correct number is?
    Using 3.20 as the index of refraction of gallium phosphide and 1.33 as the index of refraction of water:
    sin(theta) = (3.20 * sin(8.0 degrees)) / 1.33
    theta = 19.56 degrees (incorrect)

    Each time I'm submitting this question, it says my answer is within 10% of the correct answer, leading me to think that it's an error with the refractive index value.

    Thank you!!!
  2. jcsd
  3. Apr 4, 2016 #2


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    This from Wikipedia:

    Refractive index (n): 3.02 (2.48 µm), 3.19 (840 nm), 3.45 (550 nm), 4.30 (262 nm)

    What's a nominal wavelength for light?
  4. Apr 4, 2016 #3
    Okay, so from what I understand, it changes based on the wavelength...does that mean that I would just look at the wavelength of the value of 1.33 value for water? At 589.29 nm, water has a refractive index of 1.33. The closest wavelength to that value from the ones you have would be the one at 550 nm, or 3.45.
  5. Apr 4, 2016 #4


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    Try it.
  6. Apr 4, 2016 #5
    Yes, that was right!!! Thank you so much for your help!!! :smile:
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