Question

Question #490a9

Answer 1

`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.