Finding index of refraction using wavelength and 2 angles?? I'm not sure how to do a problem that involves a light ray striking a block/air interface, how to find the index of refraction of a transparent material when given the wavelength, the angle the light ray makes with respect to the normal when it enters and when it exits. It's worded like this. Model the following problem: A light ray of wavelength (lambda) propagates in a transparent block of material and strikes a block/air interface at q1 to the normal When it emerges into the surrounding air it makes a q2 angle with the normal. What is the index of refraction of the material? Test your model. It is actually a programming assignment but that's not important now I'm just not sure which formulas (I'm sorry but formulae just looks and sounds way too nerdy) to use. Because the question gave 3 variables I am assuming you need to involve all 3 of them in the calculation of the index of refraction, n. I was thinking you could use Snell's law since from what i remember the index of refraction of air is constant. But then what is the point of the wavelength?