Light travels much slower in a medium. Relation between Refractive Index and Speed of Light The speed of light in a vacuum is about 30 x 10 8 m s -1. The index of refraction of a material is defined by the speed of light in vacuum c divided by the speed of light through the material v.
Furthermore refractive index values may be significantly higher in the case of infrared waves.
N c v The index of. The relationship between the speed of light in a medium and the refractive index is the following. N c v. Relative densities difference between the two objects which helps to determine the speed of light.