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Direction of travel in glass please please HELP!

  1. Mar 25, 2008 #1
    Direction of travel in glass....please please HELP!

    1. The problem statement, all variables and given/known data
    A 0.95-cm-thick layer of water stands on a horizontal slab of glass. A light ray in the air is incident on the water 58° from the normal. What is the ray's direction of travel in the glass? (Give the answer in degrees.)


    2. Relevant equations
    Nwater = 1.33
    Nglass = 1.5

    3. The attempt at a solution
    I thought this was...
    sin theta 1/sin theta 2 = n2/n1
    1.33/1.5 * sin 58 = 0.7519 then take the inverse of sin 0.7519 = 48.758 degrees
     
  2. jcsd
  3. Mar 25, 2008 #2

    G01

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    The ray is incident on the water at 58 degrees, not the glass.

    HINT: You know the angle that the ray is incident on the water. You need to use that to find the angle it is hitting the glass at.
     
  4. Mar 25, 2008 #3
    so thats just 90-58 = 32 right?
     
  5. Mar 25, 2008 #4

    G01

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    Not quite.

    The light is refracted when it passes from the air to the water. So, you are going to have to use Snell's Law and then some geometry to find the angle of incidence on the glass.
     
  6. Mar 25, 2008 #5
    oh so n1*sin 1 = n2 * sin 2
    sin^-1 (1.33 * sin 58 / 1.5) = 48.758 degrees
     
  7. Mar 25, 2008 #6

    G01

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    You indices of refraction are wrong. Remember that your two medium for this part of the problem are air and then water.
     
  8. Mar 25, 2008 #7
    woops
    sin^-1 (1.00 * sin 58 / 1.33) = 39.615 degrees
     
  9. Mar 25, 2008 #8

    G01

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    Looks good. Now you should be able to go about the problem as you did initially, but now you have the right incident angle for the glass.
     
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