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Just wondering, why is it that blue light will refract less than red light, i.e. why does the fact that blue light has a shorter wavelength mean that it will refract less at a boundary?

I read somewhere that the wavelength decreases of light as it enters an optically denser material, which seems logical given that frequency remains constant and c = f λ. Is there some sort of constant which would mean that if the wavelength of a type of light in material one is x% shorter than that of, say, red light, the wavelength after refraction would be kx% shorter?

I know this is a terribly worded question, this is all new to me and it's a bit difficult for me to put down my thought process.

Thanks in advance!

Saharsh Aanand
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  • There's a lot buried underneath the surface of your question. I'll point out that the constant you are looking for is the index of refraction defined as $n=c/v$ where $v$ is the speed of light in the medium. With that, $\lambda_{in} = \lambda_{out}/n$. The value of $n$ (or $v$) depends in a complicated way on the arrangement of atoms/molecules in the system, and the properties of those atoms/molecules. Maybe you can take it from there. – garyp Jul 14 '20 at 11:53
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    The second part of the title makes no sense on its own as nothing in the first part refers to two things or phenomena. – ZeroTheHero Jul 14 '20 at 13:00

1 Answers1

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First off - it is not necessarily the case that the angle of refraction changes with wavelength. That happens when one or both of the materials in question exhibit what's called "dispersion," meaning the index of refraction is wavelength-dependent.

Now, the dispersion of most materials is an observed and measured effect. As some comments suggest, attempting to predict a given substance's dispersion from first principles is quite difficult if not impossible.

You are correct that the frequency remains constant while the wavelength changes inside a given material.

Rather than repeat other answers or quote hunks from references, I'll just suggest you start with Wikipedia pages and then perhaps move on to Smith, "Modern Optical Engineering."

Carl Witthoft
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