Refraction of an EM Wave n air = n water =1.33 Index of refraction n = c/v Direction of propagation bends toward the normal axis going from 1 medium (lower n) to a denser medium (higher n) Bending occurs because one part of the wave ‘lags’ the other. Wavelength shortens going from media of lower n to higher n by a factor of 1/n Other indices: Vacuum Ice 1.3 Glycerine Glass Ethyl alcohol 1.36 Normal axis ii  refr <  i

Going the other way, from large to small n Depending on angle, you can have refraction OR none at all Total Internal Reflection

What makes a Rainbow ? Blue is refracted more than red (dispersion) at A Total internal reflection occurs at B Blue is refracted more than red at C A B C Observer sees red from higher raindrops and blue from lower raindrops.

Rainbows from Soap Films & Oil Slicks

Colors have different wavelengths Their phases change because of the thickness of the film, and the discrete 180  phase change Reflected rays of same color interfere differently, leading to rainbow patterns.

How do waves add/subtract ? In phase Out of phase