Hello, As we all know, speed of light of different wavelengths (let's say red and blue) in vacuum is same. However, in medium (like glass) it's different and depends on a wavelength and a refractive index. Let's say we send a short pulse of white light incident into a piece of glass (of length L). Red light will come out of it first and a blue last. But how can I calculate the time difference (or a displacement) of red and blue light at the exit from the glass? I know the velocity in medium is v=c/n, where c is constant (speed of light in vacuum) and n is a refractive index of the medium. But how can I get a relation between v (speed of light in medium) and its wavelength? I guess I need to connect between refractive index n and a wavelength of the light first. Thought to use a Cauchy's equation (or a Sellmeier equation), but maybe there is a easier way? Thanks!