Asked by shekhar14351 | 16th Feb, 2010, 09:59: AM

Expert Answer:

Dear student,

Any ray making an  angle less than about 40° with the water surface from below is totally reflected. To a fish, or a diver, the water surface looks like a perfect mirror, except for the “hole” directly overhead in which the entire sky is imaged.

If you open your eyes under water (swimming pools work better than the ocean, here, as the water is clearer) and look up, you'll see that the whole hemisphere of sky above the water is imaged into a cone with a vertex angle a little larger than 90°. The horizon of the world above water appears well above the horizontal under water. If we forget about waves for a moment, and just have a calm, flat water surface, it looks something like this:

Here the solid rays show how the whole 180° of sky above the water is imaged into a much smaller angle below the water. The remaining directions in the water, below the image of the horizon, are rays that are totally reflected back into the water, as shown by the dashed lines.

Hope this helps.

Answered by  | 16th Feb, 2010, 02:00: PM

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