Question

Let us list some of the factors, which could possibly influence the speed of wave propagation:
(i) nature of the source.
(ii) direction of propagation.
(iii) motion of the source and/or observer.
(iv) wavelength.
(v) intensity of the wave.
On which of these factors, if any, does

(a) The speed of light in vacuum

(b) The speed of light in a medium (say, glass or water), depend?

Answer 1

The speed of light in vacuum is a universal constant independent of all the factors listed and anything else. In particular, note the surprising fact that it is independent of the relative motion between the source and the observer. This fact is a basic axiom of Einsteins special theory of relativity.

The speed of light in a vacuum which is $3\times {10}^{8}m/s$ is a universal constant. It is not affected by motion of source, the observer, or both. Hence, the given factor does not affect the speed of light in a vacuum

Out of the listed factors, the speed of light in a medium depends on the wavelength of light in that medium.