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Homework Help: Radiation intensity and distance?

  1. Aug 19, 2008 #1
    1. The problem statement, all variables and given/known data
    A light ray enters the plastic block in the illustration at an angle of 33.0° and then exits the opposite side. The long side of the block has a length of 0.670 m and its index of refraction is 1.70. For how much time is the light ray inside the block?


    2. Relevant equations
    Snell's law:
    n=index of refraction
    [tex]\theta[/tex]=incident angle from normal

    n plastic=1.70
    n air = 1.00

    3. The attempt at a solution
    According to Snell's law:
    arcsin(0.92588636)=[tex]\theta[/tex] = 67.8023923 degrees

    And the speed of light is 2.998*10^8 m/s.

    But after that I am not sure where to proceed! Can anyone help me figure this one out?
  2. jcsd
  3. Aug 19, 2008 #2


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    Homework Helper
    Gold Member

    You need to know two things to solve this problem.

    1. The speed of light in the plastic block.

    Do you know how to find this?

    2.You need to know the length of the path traveled through the block.

    You should be able to find this using the angle obtained from Snell's law and some trigonometry, but I can't say for sure if you don't post the actual figure in question.
  4. Aug 19, 2008 #3
  5. Aug 20, 2008 #4
    Got it. Speed of light in plastic. Roger. Appreciate it
    Last edited: Aug 20, 2008
  6. Aug 20, 2008 #5


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    Homework Helper

    The only property you're given about the material is its index of refraction. What is the definition of the index of refraction?
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