This business about the speed of light changing really bothers me because it isn't true. The speed of light is a constant in all reference frames. The velocity changes as light enters into a medium because it doesn't travel a straight line through the material. This phenomenon is what gives rise to the index of refraction. It's also what leads to dispersion, since the index of refraction is actually a function of frequency - this is a second-order effect which is not usually taught in introductory physics courses, but explains how prisms work.
What's really going on here is that the velocity that light travels in a medium is actually dependent upon its energy (or frequency, or wavelength - all three terms are describing the same quantity), therefore the index of refraction is dependent upon the energy as well.
I want to also point out that the BR use of wave velocity is imprecise and dangerous - they could be referring to the phase velocity or the group velocity, which are not the same, in general. So, don't get too caught up on the terminology.
Here's what I would know for the MCAT:
- Don't think of light as a wave - think of it as a shower of particles called photons that all carry energy, spin, and momentum.
- The energy of a photon is given by the equation I cited earlier.
- Wavelength, frequency, and angular frequency are all measuring the same fundamental thing, energy, thus they are not independent quantities in any way.
- The speed of light is a constant in all reference frames.
- The path that light travels in a medium depends upon the material as well as the energy of the photon.
- The index of refraction for a medium is given as the ratio of the speed of light (constant) to the velocity of light in that medium
- Because of #5, the index of refraction for a medium will depend upon the frequency of the light
I think if you understand these things, you'll be set.
I realize that thinking of light as a bunch of particles runs counter to what they tell you in physics class. This is because physics teachers love to talk about wave-particle duality, but they almost always do a bad job of explaining what that means. The one place thinking of light as a wave makes sense is when working diffraction or interference problems. For most people, description of these phenomena using the wave model of light is more intuitive - a particle model can be made, but it's a lot less intuitive.