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Optics - Beam illuminating coin under water

  1. Dec 10, 2005 #1
    A coin lies on the bottom of a pool under 1.5 m
    of water and 0.90 m from the side wall as shown
    in Figure 2. If a light beam is incident on the
    water surface at the wall,at what angle relative
    to the wall must the beam be directed so it will
    illuminate the coin. Ans: 28.90

    The answer I get is 43.29, different with the given answer? May I know which answer is correct actually?
  2. jcsd
  3. Dec 10, 2005 #2


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    I don't see a diagram ... but if :
    the ray's angle in the water (measured from the vertical) is about 31 degrees,
    then the ray's angle in air (measured from the vertical) is about 43.18 degrees.
    Are they REFLECTING the ray off the wall? (I expected this to be a refraction)
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