UPSC NDA 2 2016 General Ability Solved Paper

Concept:When light passes from one medium to another, its frequency stays constant because it is determined by the source.Only the speed and wavelength change due to the change in the medium's optical density.Explanation:Step 1: Light enters a glass slab from air — from a rarer to a denser medium.Step 2: The speed of light decreases in the denser medium.Step 3: Frequency ($f$) remains unchanged because it depends on the source, not the medium.Step 4: Wavelength ($λ$) changes because $v = f λ$, and $v$ changes while $f$ is constant.Step 5: Thus, option A (only frequency changes) is wrong.Step 6: Option B (frequency and velocity both change) is wrong because frequency does not change.Step 7: Option C (frequency does not change) is correct.Step 8: Option D (frequency and wavelength both change) is wrong because frequency remains constant.Answer:Option C: Frequency does not change.