# Light dispersion in water

Simple question: Water is clearly not disspersive if we have it, for example, in a glass of water. We don't see the rainbow through a glass of water. However drops of water disperse light in the atmosphere and allow us to see the rainbow, am I right? Why is this? In which conditions is water disspersive and in which conditions it's not?.

• I see rainbows in glasses of water! A narrow beam of reflected sunlight passing through the glass about half way between the center and edge will do the trick. – uhoh Jun 3 '17 at 16:51

The dispersion that leads to the rainbow effect generated by transparent media results from an intrinsic property of the medium being considered: the dependence of its refractive index $n$ on the wavelength of light $\lambda$ passing through it. In this sense, water in a glass is just as dispersive as water droplets in a rainbow.