Question

Why was your measured refractive index different from the value given in the lab report?

Answer 1

Consider a material like glass (mostly SiO2) that has some impurity (like sodium, Na, which is added intentionally, so not exactly an impurity, but never mind that detail). As I'm sure you know, Na strongly emits (in a flame or a discharge) a bright yellow light; you probably also know that if it emits light of this color it also absorbs it. In the glass there's not much opportunity for it to emit, but it can (and does) still absorb it. But then what? Usually it will re-emit it, after a short delay. This delay affects the macroscopic (apparent) velocity of light in the glass, which is a (reciprocal) measure of the index of refraction. The closer the wavelength of the light to the color of this "resonance" the longer the delay, the smaller the apparent velocity, so the larger the index of refraction. Of course this intuitive model runs roughshod over all sorts of wave/quantum mechanics concepts, i.e., it oversimplifies crucial concepts like phase shift, but I hope that with this simple "mechanical" model in mind, maybe it will be easier for you to follow up on the references others have given and eventually understand what is happening at a deeper but unavoidably more formal level.

So,there are a lot of factors on which the refractive index depends,so this is the reason the measured refractive index is different from the value given in the lab report.

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