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Q & A: Diffraction vs. refraction

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Most recent answer: 11/26/2013
Why do longer wavelength sound waves diffract more around objects while shorter wavelength light waves refract more through a prism? Seems to me an inconsistency of any wave theory. I would expect the degree of bending to be consistent with the relative length of the wave regardless of light or sound.
- Greg (age 45)
Guelph, ontario, canada

A very nice question, Greg.  The problem is that diffraction is strictly a geometrical wave phenomenon whereas refraction is a problem that involves the variation of the index of refraction of glasses with respect to the wavelength.  I found this graph of indicies of refraction of various glasses on the web at .  It shows that in general the index of refraction  increases as the wavelength becomes shorter.  Now since the refraction angles are related by   sin(θ2) = sin( θ1) n1/n2  you get this inversion.

Wave theory still rules!



(published on 11/26/2013)

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