I'm a bit confused on the topic of refraction, some starting premises:

1) When light refracts from exiting a medium with a low n and entering a medium with high n the light bends.

2) The index of refraction, n, supposedly is lower for longer wavelengths than others (why exactly this is, is difficult to understand) which is why we have chromatic dispersion of white light. I.e. although we're given n for certain substances, n is actually wavelength dependent

3) The speed of light slows down when traveling in media with higher index than 1 (vacuum).

4) Frequency of a light wave doesn't change as it enters a new medium


Because of 3 and 4, wavelength must decrease if the speed light travels in a medium decreases. what does this mean for the color of light? wavelength has changed but the frequency hasn't. E.g. do we perceive red colored light in the air the same as red if we view it underwater?? (maybe another way of asking this is, does the color change as light passes through different media)

If light underwent refraction from air to water for instance (1), what happens if there's another medium? From 2, n would differ with different "wavelengths" but would you use the new wavelength after it passed through the water or would you use the wavelength from the light as if it were in a vacuum?? (i.e. is it really "wavelengths" that determine these differing n's or is it the frequency)

If someone can give an easy to understand explanation WHY n would differ with different wavelengths ie #2 (also why isn't it said that n differs with frequency??)

If this sounds confusing please ask me to clarify or restate my questions


  • $\begingroup$ Your first question is a duplicate of What determines color — wavelength or frequency? and the questions linked to it. I'd suggest removing that and just focusing on the other main question: Is it wavelength or frequency that determines refraction? $\endgroup$ – user10851 Jul 1 '14 at 2:09

This same question confused me a lot "when I was just a lad". Your eye responds to the frequency of light, not the wavelength. Whatever happens to the wavelength between source and retina is immaterial to the color. The frequency does not change, as you point out in (4).


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