question_answer

A light is incident on face AB of an equilateral glass prism ABC. After refraction at AB, the ray is incident on face BC at an angle slightly greater than critical angle so that it gets reflected from face BC and finally emerges out from face AC. Net deviation angle of the ray is \[112{}^\circ \]anticlockwise. The angle of incidence 't? has value      

A) \[22{}^\circ \]              

B)        \[24{}^\circ \]

C) \[26{}^\circ \]              

D)        \[28{}^\circ \]

Correct Answer: C

Solution :

[c]                       Net deviation \[\delta =(i-r)+180-2{{\theta }_{c}}+i-r\] \[112=2(i-r)+180-2{{\theta }_{c}}\]                 ...(1) and \[{{\theta }_{c}}+r=60{}^\circ \]                             ...(2) From (1) and (2), \[i=26{}^\circ \]