UPSC CSE Prelims 2001
When light propagates from one medium (e.g., air) to another medium with a different optical density (e.g., glass), its speed and wavelength change.
The velocity of light decreases when it enters a denser medium like glass from a rarer medium like air, due to the higher refractive index of glass.
The wavelength of light is directly proportional to its velocity (v = fλ, where f is frequency and λ is wavelength). Since velocity decreases, the wavelength also decreases proportionally.
However, the frequency of light is determined by its source and remains constant regardless of the medium through which it travels. It is an intrinsic property of the light wave itself.
Therefore, only the wavelength and velocity of light are affected when it passes from air to glass.
(a) This option is incorrect because the frequency of light does not change when it passes from one medium to another.
(b) This option is incorrect as it states that frequency changes, which is not true. While velocity does change, frequency remains constant.
(c) This option is incorrect because it includes frequency as a variable that is affected, whereas frequency remains unchanged during the transition of light between media.