Question 14

# 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) Wave length.(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?

(a) Speed of light in vacuum is an absolute constant, according to Einstein’s theory of relativity. It does not depend upon any of the factors listed above or any other factor.

(b) The speed of light in a medium like water or glass

(i) does not depend upon the nature of the source.

(ii) does not depend upon the direction of propagation, when the medium is isotropic.

(iii) does not depend upon motion of the source w.r.t the medium, but depends on motion of the observer relative to the medium.

(iv) depends on wavelength of light, being lesser for shorter wavelength and vice-versa.

(v) does not depend upon intensity of light.