Physics: Optics and Sound: UPSC Previous Year Questions (Science and Technology)
11 previous year UPSC Prelims questions on optics and sound appear here, from 1996 to 2009. UPSC asks which waves night vision uses, how light scatters in the atmosphere, what changes when light enters glass, what noise levels mean and why a CD shows rainbow colours. The explanations give the principle in words.
Explanations state facts as of the year each question was asked; words like “recently” refer to that year.
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UPSC 1996Science and Technology · Physics: Optics and Sound
Q11. Total internal reflection can take place when light travels from:
Explanation
Total internal reflection occurs when light travels from a medium with a higher refractive index to a medium with a lower refractive index, and the angle of incidence exceeds the critical angle. From the given options, total internal reflection can take place when light travels from Diamond to glass. This is because diamond has a higher refractive index than glass, so when light travels from diamond to glass, it can undergo total internal reflection if the angle of incidence is greater than the critical angle.
Answer key for these questions
Q
UPSC year
Correct answer
11
1996
(a) diamond to glass
What UPSC has tested in Physics: Optics and Sound
Infrared waves are used in night vision apparatus.
Light of shorter wavelengths is scattered much more than light of longer wavelengths.
When light passes from air to glass, its wavelength and velocity change, but not its frequency.
Diffusion of light in the atmosphere takes place due to dust particles.
The rainbow colours of a CD in sunlight arise from refraction, diffraction and reflection.
Frequently asked questions
How many previous year UPSC questions are there on Physics: Optics and Sound?
This page covers 11 previous year UPSC Prelims GS Paper-I questions on Physics: Optics and Sound (Science and Technology), asked from 1996 to 2009. Each has the correct answer and an explanation.
Which waves are used in night vision devices?
Infrared waves. Objects emit infrared radiation according to their temperature, and night vision devices detect it and convert it into a visible image, so they work without visible light.
Why does the sky look blue?
Because shorter wavelengths such as blue are scattered much more by air molecules than longer wavelengths such as red. This Rayleigh scattering spreads blue light across the sky, which is why it appears blue during the day.
