Q. 204.0( 4 Votes )

A. A ray of light

Answer :

Given: -


Minimum deviation, = 30o


Prism is equilateral



Formula: -


The Refractive index of the prism in terms of minimum deviation is found as,



Where, is called the minimum deviation, and A is called the angle of the prism.


Calculation: -





Hence,



Also, we know that,




So,




Conclusion: -


the velocity of light in the given prism is, 2.12 × 108 m/s.


B) For emerging ray to graze along face AC,



TIR must occur on the face AC, so,



Hence, rAC = 45o


Also, in quadrilateral AQNR,



As, Q = R = 90o,


A + N = 180o


As, A = 60o , N = 180o – 60o = 1200


Also,




Applying Snell’s law on face AB,





Hence for grazing incidence on face AC,


SiniAB=√2× sin(15o) =1.414× 0.2588=0.366


SiniAB=0.366


iAB=21o (approx.)


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