Question

WHAT IS THE RELATION BETWEEN REFRACTIVE INDEX AND OPTICAL DENSITY

Answer 1

The optical density of a medium is not the same as its physical density.The physical density of a material seems to be mass/volume ratio.Optical therefore determines how much light wave is slowed down as it passes through a medium.The more slower that a wave will move through the material the more optically dense a material is.
The refractive index is measured of optical density.A medium with a low optical density,would have also a low refractive index.e.g air ,having a low optical density has a refractive index of 1.0003,whereas water,with a higher optical density,has a higher refractive index of 1.333