Why white light splits into different colours when it passes through a prism ?

Explanation

1) The speed of light is constant in vacuum for all colours, but it depends on the wavelength of light when it passes through a medium.
2) We know refractive index of a medium depends on wavelength of light.
3) When white light passes through a medium, each colour selects its least time path and we have refraction of different colours to different extents.
4) This results in seperation of colours, producing a spectrum.
5) It has been experimentally found that refractive index decreases with an increase in wavelength.
6) In VIBGYOR , red colour has longest wavelength and violet colour has shortest wavelength. The refractive index of red is low, hence it suffers low deviation.