Q6 of 26 Page 1

A ray of light incident on an equilateral glass prism propagates parallel to the base line of the prism inside it. Find the angle of incidence of this ray. Given refractive index of material of glass prism is .

OR


A biconvex lens of glass of refractive index 1 �5 having focal length 20 cm is placed in a medium of refractive index 1 �65. Find its focal length. What should be the value of the refractive index of the medium in which the lens should be placed so that it acts as a plane sheet of glass?


Here, we have a case of minimum deviation.

We know, the prism angle,


Refractive index,


Let the angle of incidence be and that of refraction be


Therefore,






OR


Given, Refractive index of lens,


Refractive index of medium,


Focal length of lens,


Let the focal length in the medium be . Let the two radii of curvature be and .


We know





Now, the focal length in medium would be





For lens to act as a plane sheet of glass, the refractive index of the medium should be same as that of the lens, that is 1.5.


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