Light falls from glass (μ = 1.5) to air. Find the angle of incidence for which the angle of deviation is 90°.

Refractive index of glass is


Angle of incidence=i


Light ray is passing from glass to air i.e. from denser to rarer medium.


We know that;


Critical Angle=


=


Maximum angle of deviation in refraction is=


In reflection,


Deviation =


Or,



So, the angle of incidence=.


1