Question

Direction:- Q.9 i, ii and iii are based on the given paragraph. The refractive index n of an optical medium is defined as the ratio of the speed of light in vacuum, c = 299792458 m/s, and the phase velocity v of light in the medium, n=c/v. The phase velocity is the speed at which the crests or the phase of the wave moves, which may be different from the group velocity, the speed at which the pulse of light or the envelope of the wave moves.The definition above is sometimes referred to as the absolute refractive index or the absolute index of refraction to distinguish it from definitions where the speed of light in other reference media than vacuum is used. Historically air at a standardized pressure and temperature has been common as a reference medium.

Option 1

Clear selection

Q9 (i) The refractive index of transparent medium is greater than one because *

(a) Speed of light in vacuum < speed of light in tansparent medium

(b) Speed flight in vacuum = speed of light in tansparent medium

(c) Frequency of light wave changes when it moves from rarer to denser medium

(d) Speed of light in vacuum > speed of light in tansparent medium

Q9. (ii) The refractive index of water is 1.33. The speed of light in water will be *

(a) 1.33 × 108 m/s

(b) 3 × 108 m/s

(c) 2.26 × 108 m/s

(d) 2.66 × 108 m/s

Q9 (iii) You are given three media A, B and C of refractive index 1.33, 1.65 and 1.46. The medium in which the light will travel fastest is *

(a) A

(b) B

(c) C

(d) equal in all three media

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Answer 1

x

c is

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