1. Refraction of an EM Wave n air =1.0003 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 1.000 Ice 1.3 Glycerine 1.473 Glass 1.5-1.75 Ethyl alcohol 1.36 Normal axis ii  refr <  i

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

3. 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.

4. Rainbows from Soap Films & Oil Slicks

6. 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.

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