I'm having difficulty understanding why light slows down in a medium. One explanation I found says the electric and magnetic fields in the light beam cause the electrons in the material to oscillate which creates other electromagnetic waves. These other electromagnetic waves and the light superimpose giving a wave travelling slower than c.
We were taught in class that light obeys the superposition principle and that it acts similarly to waves on a rope; when two waves are made at either end they eventually cross paths, each wave moves as though the other one isn't there and when they meet they superimpose. But this superposition doesn't affect the individual constituent waves so they each continue on and just pass through one another.
If the EM waves created by the electrons superimpose with the light, shouldn't the constituent parts of that superimposed wave continue to move on as though the other waves aren't there? Why doesn't the light just pass through these waves at speed c? If EM waves are different enough to a rope, such that the superposition does affect the individual constituent waves, then why does light still travel at c once it leaves the material? If there are all these other waves that have been created by the electrons why do they not 'decide' to leave the material along with the original light so that the superposition remains and the wave travels at less than c?
I'm a second year university student so it would be helpful if the explanations could be kept to an undergraduate level.
