Question #490a9

1 Answer

#3xx10^8m//s#

Explanation:

By Einstein's postulates, the speed of light is constant and the same under all conditions in air or vacuum and has value

#c=3xx10^8m//s#.

The precise value in vacuum is #299792458 m//s#, but for most practical purposes, it's ok to round to 3 significant figures: #3.00xx10^8m//s#. The speed of light in air is actually slightly slower than in vacuum at #29970000m//s#, about #90km//s# slower, but this value also rounds to the same at 3 significant figures.

This is because as light enters a different medium of higher optical density than vacuum, its speed slows down and as a result it may be refracted or dispersed, depending on the angle of incidence and relative refractive indices between the 2 different media.