Question

Sunlight reaches to us in composite form and not in its constituent colours because
I. vacuum is non–dispersive.
II. speed of all colours is same in vacuum.
III. light behaves like a particle in vacuum.
IV. light travels in a straght line in vacuum.
(a) I and II (b) II and III (c) III and IV(d) I and IV

Answer 1

 (a) The variation of refractive index with wavelength may be more pronounced in some media than the other. In vacuum, of course, the speed of light is independent of wavelength. Thus, vacuum (or air approximately) is a non dispersive medium in which all colours travel with the same speed. This also follows from the fact that sunlight reaches us in the form of white light and not as its components. On the other hand, glass is a dispersive medium