Hi I'm trying to sort this concept out in my head and have reached a stumbling block!! 1. ok so light travels through medium a and transmits through medium b and refracts. The angle or refraction is given by snell's law, and quantified by the refractive index of materials a and b. 2. But I now understand that the refractive index n of a material is not a static thing; rather, it varies depending on which wavelength light passes through it. 3. BUT ALSO, for light passing from material a to material b, its wavelength changes!!!! According to this equation: wavelength through medium = wavelength through vacuum/index of refcraction 4. frequency is constant (waves cannot be destroyed by a medium, right? can you elaborate on this by teh way????). 5. question: if we take a red beam of light passing through a vacuum (with it's characteristic wavelength), and then refract it through a prism, from (3) it would appear that it's wavelength changes, and so does this mean it's not red anymore? or is the quality we observe as colour purely governed by the frequency which is constant? Cause often enough colours are indexed by wavelength!!!!???? That is, does a red beam through a vacuum hit a prism, refract, have its wavelength changed and consequently appear to be yellow or something???? 6. Please look at the following: wavelength of light in some medium = w (not lamda) wavelength of light in vacuum = w_0 refractive index: n = c/v (i) in some medium, the speed of light is given by v = fw (ii) in vacuum, the speed of light is given by c = fw_0 (iii) from (i) and (ii), n = C/(fw) (iv) BUT TAKE A BEAM OF LIGHT WITH VACUUM WAVELENGTH w_0, AND LET IT PASS THROUGH A MEDIUM WITH INDEX OF REFRACTION n, THEN THE IT'S WAVELENGTH CHANGES FROM w_0 to w according to the following: w = w_0/n (v) But now from iv and v, I get n = w_0/w and n = c/(fw) so c/(fw) = w_0/w and rearanging, c = fw_0 which is correct, but kind of circular. I don't know my head seems to be in a mess! 7. What I'm trying to convey is my desire to understand the whole process: does the wavelength change when light crosses from material a to b BECAUSE of the refractive index which is a measure of how much slower the speed of light is in that medium? or is it the refractive index which responds to the particular specific wavelength in question (as required for dispersion). Because the two don't sit well TOGETHER in my head as that would seem to create a situation where a beam of light hits a medium, refracts because of an index of refraction, which is itself determined by the wavelength, which by the way changes once it's being transmitted because of the refractive index. DO YOU SEE MY CONFUSION?? THANK YOUUUUU!!!!