How is the speed of light related to optical density?

The speed of light is inversely proportional to optical density. That is; as the optical density increases, the speed of light decreases. How does this happen? Let's discuss physics!

The speed of a lightwave depends on the properties of the material medium. In the case of electromagnetic waves, the speed of the wave depends on the optical density of the material medium. This optical density is different from the physical density.

Optical density refers to the extent to which electromagnetic wave energy can be hindered by the atoms of the material medium in the form of vibrating electrons before it re-emits it back as an electromagnetic disturbance. The higher the optical density increases a material, the lower the speed of the electromagnetic wave in that material. A good indicator of optical density through a medium is refractive index. And the optical density increases as the refractive index increases, thus leading to a decrease in the speed of light through that medium.

To find out how the speed of light is related to optical density, we first have to figure out the refractive index of the medium in which the light is passing through. In a vacuum, light travels around roughly 300,000 kilometers per second, giving it a refractive index of 1. When light is traveling through water, it slows down to approximately 225,000 kilometers per second, which gives us a refractive index of 1.3. Light travels even slower when it's passing through glass,(200,000 kilometers per second) with a refraction index of 1.5.

In short, when the speed of light is slower passing throughair, than the medium the light is passing through is denser than air. When the speed of light is faster when passing through air, than the medium the light is passing through is more dense than the air is.