BharatNotes Refraction
nounUsage in a UPSC answer
Just as a single ray of light undergoes refraction when it crosses from one medium into another, a uniform central policy is often refracted through the prism of local institutions, emerging in implementation as something quite different from its original design.
Synonyms
Antonyms
Word Family
refract (v), refractive (adj), refracted (adj), refractivity (n), refractometer (n)
Root
Latin refringere = to break up; re- = back + frangere = to break; Late Latin refrāctiōnem = a breaking back
Etymology
From Late Latin refrāctiōnem, from Latin refringere ("to break up"), from re- ("back") + frangere ("to break").
Memory Hook
Re-FRACT-ion shares its root with FRACTURE and FRACTION, all from Latin frangere 'to break': light's straight path is "broken" and bent as it enters a new medium.
How This Word Works in UPSC Writing
The bending of light on passing into a medium of different optical density, caused by the change in its speed. The detail most often stated backwards is that the frequency stays the same across the boundary while the wavelength and speed change, since frequency is set by the source and cannot alter at an interface. The refractive index is simply the ratio of the speed in vacuum to the speed in the medium. Its everyday consequences are worth listing, because they recur as questions: a stick appears bent and a pool appears shallower than it is; the Sun is visible for a few minutes before it has actually risen and after it has actually set, because atmospheric refraction lifts its apparent position; and stars twinkle while planets do not, because a star is effectively a point source whose light is disturbed by atmospheric turbulence, whereas a planet is an extended disc whose many points average out.
Don’t Confuse It With
Refraction is bending caused by a change of speed entering a new medium, while reflection is bouncing back from a surface. Total internal reflection occurs when light travelling towards a rarer medium meets the boundary beyond the critical angle and is reflected entirely, which is the principle of optical fibre and of the brilliance of a cut diamond. Dispersion is refraction that separates colours, arising because refractive index varies slightly with wavelength. In refraction the frequency is unchanged while wavelength and speed both change.
Hindi Meaning
अपवर्तन (apvartan); पूर्ण आंतरिक परावर्तन for total internal reflection.
Common Questions
- Does the frequency of light change during refraction?
- No. The frequency is fixed by the source and stays the same, while the speed and wavelength both change in the new medium.
- Why do stars twinkle but planets do not?
- A star is so distant that it acts as a point source easily disturbed by atmospheric refraction, while a planet presents a small disc whose many points average out the fluctuations.
Seen in UPSC Question Papers
- Prelims 2016 — Physics
- Prelims 2013 — Physics
Real UPSC previous-year questions whose text uses “Refraction” — proof this word earns its place on your list.
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