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Homework Help: Point source of light beneath water.

  1. Sep 7, 2006 #1
    A point source of light is 245.0 cm below the surface of a body of water. Find the diameter of the circle at the surface through which light emerges from the water.

    Can someone give me a push start as to how to approach this problem? I can't figure it out for the life of me.

    I know that v=c/n, and using 1.33 at the index of refraction of water, I can find the velocity of the light as it reaches the surface is 2.3E8m/s. The point source will emit light isotropically in all directions, and I have the distance to the surface... but for the life of me I can't find how to relate this to the diameter of the circle it will leave on the surface.
  2. jcsd
  3. Sep 7, 2006 #2


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    Staff: Mentor

    Does your text cover "total internal reflection"? That's the reason why light that is angled way out to the side won't make it out of the water....
  4. Sep 7, 2006 #3
    Thank You. Im such a bonehead sometimes.
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