A diver is inside a swimming pool. What colour would he observe inside the pool if a light source of green colour is kept outside the pool. My textbook says that he observes blue colour. But I think the answer should be green.How should I approach this problem?I thought that colour is a direct result of frequency but this question changes that notion.
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When the light passes through a different medium, its frequency remains constant even though its velocity and wavelength change. The energy of a photon is dependent only on its frequency. So light should have the same colour in different media. So it should not change colour for an observer inside a swimming pool.
After thinking for a while, I concluded why the book says that the colour should be blue. Since the velocity decreases and the wavelength decreases as the frequency is constant, the author assumed that the colour depends on wavelength in different media and said that the colour observed underwater will be blue. But colour perception is dependent on the frequency of light, not wavelength. So the answer is probably incorrect.
Here is a discussion on colour perception.
Mechanic
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Especially it enters the eye of the diver which is always the same medium. More interesting could be a refraction gate under water. (or a resonant Dipol) – lalala Sep 12 '21 at 10:17