IIT JEE , AIEEE Forum - Physics , Optics

nibin89

THE MAXIMUM VALUE OF INDEX OF REFRACTION

OF A MATERIAL OF A PRISM WHICH ALLOWS THE

PASSAGE OF LIGHT THROUGH IT WHEN THE

REFRACTING ANGLE OF THE PRISM IS 'A' IS

a)(1-sinA/2)^1/2 b)(1-cotA/2)^1/2

c)(1-(tanA/2)^2)^1/2 d)(1+(cotA/2)^2)1/2

krishna.gopal

d) is the right answer.

Most difficult situation for light to pass a prism is when it hits surface at 90 degree and goes such that it is parallel to base of prism (same as in the case of minimum deflection)

So angle (i) = 90 degree
angle (r) =sin(A/2)
1*sin(90)=n*sin(A/2)
No passage will take place if
n>1/sin(A/2) = cosec(A/2) = sqrt(1+cot^2(A/2))

There is another way to look at it. Light will always pass through a glass slab which can be considered as a prism with zero angle of prism. So for A = 0 answer should be infinite and only d) satisfies that

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