which is about 19°.
Notice that θ 2 < θ 1 , as we would expect, since the refracting medium (glass) has a
greater index than the incident medium (air).
Dispersion of Light
One thing we learned when we studied waves is that wave speed is independent of
frequency (Wave Rule #1). For a given medium, different frequencies give rise to
different wavelengths because the equation λf = v must always be satisfied and v
doesn’t vary. But when light travels through a material medium, it displays
dispersion, which is a variation in wave speed with frequency (or wavelength). So,
the definition of the index of refraction, n = c/v, should be accompanied by a
statement of the frequency of the light used to measure v, since different frequencies
have different speeds and different indices. A piece of glass may have the
following indices for visible light.
Notice that as the wavelength decreases, the refractive index increases. In general,
higher frequency waves have higher indices of refraction. Most lists of refractive