The velocity of different frequency light in a fixed medium is different. In other words the index of refraction of different light in a given medium is different. This fact could explain chromatic dispersion. But why? What physics can explain this phenomena? I realise that in the vaccum, all light travel at a fixed speed. So the difference in speeds in a material must be because of the material and not an intrinsic property of light. I notice that light of higher frequency has a higher index of refraction compared to lower frequency light. This could be due to higher frequency light more frequently colliding with the atoms in the material hence appear to pass the material slower. Thereby having a higher refracting index. Correct? Consider violet and red light through a rain drop. Both ligh pass equally as much and as diverse through the rain drop but the observer at a fixed location will only see both light when they constructivly interfere with themselves. For violet light, this means appearing closer to the normal of incidence because they will probably not have shown straight through but follwed a curved path due to colloisions hence have travelled a distance more than what it seems. For red light, it means further from the normal because they colloide less and have mostly shown 'straight on' through the material. Finally the distance both light have travelled should be about equal (although coming out at different locations and that is why we see chromatic dispersion). Is this a correct explanation?