In addition the speed of light through a material of the refractive index set by the slider is calculated and displayed beneath the block. The velocity of light in glass whose refractive index with respect to air is 15 is 2 1 0 8 ms 1. C 299792458 speed of light in a vacuum in.
V 299792458 133.
One indicator of the optical density of a material is the index of refraction value of the material. V c n. V c n 30 x 10 8 m. Different media reduce that speed by different amounts depending on their optical density.