1995 General Studies, all questions
UPSC Prelims 1995 · General Studies
Question 111: Science and Technology
Optical fibre works on the principle of
atotal internal reflection
brefraction
cscattering
dinterference
AnswerThe answer is (a).
An optical fibre is a thin strand of glass or plastic with a core of higher refractive index surrounded by a cladding of lower index. Light entering at a suitable angle strikes the boundary beyond the critical angle and is totally reflected again and again, travelling along the fibre with little loss, even around bends. Remember: an optical fibre works by total internal reflection.
Why each option is right or wrong
- (a) Right: total internal reflection.
- (b) Refraction bends light at the entry but does not keep it inside.
- (c) Scattering would cause loss of light, the opposite of what the fibre needs.
- (d) Interference is not the working principle of fibres.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 1995, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.