2001 General Studies, all questions
UPSC Prelims 2001 · General Studies
Question 104: Science and Technology
When light waves pass from air to glass, the variables affected are
aWavelength, frequency and velocity
bVelocity and frequency
cWavelength and frequency
dWavelength and velocity
AnswerThe answer is (d).
When light passes from air into glass its frequency stays the same, because frequency is fixed by the source. The speed falls, since glass has a higher refractive index, and the wavelength falls in the same proportion (v = f x wavelength). So wavelength and velocity change, but not frequency. Remember that the frequency of a wave never changes when it crosses a boundary.
Why each option is right or wrong
- (a) Frequency does not change.
- (b) Frequency does not change, and wavelength does.
- (c) Frequency does not change, and velocity does.
- (d) Right: wavelength and velocity change.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2001, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.