A ray R1 is incident on the plane surface of the glass slab (kept in air) of refractive index √2 at an angle of incidence equal to the critical angle for this air glass system. The refracted ray R2 undergoes partial reflection and refraction at the other surface. The angle between reflected ray R3 and the refracted ray R4 at that surface is :
Since, it is given that angle of incidence is equal to the critical angle
Therefore,
sini=1n=1√2
i=45∘
According to laws of refraction
sinisinr=n(refractiveindex)
sinr=sinin=12
r=30∘
Let θ is the angle between R3 and R4
So, θ=180∘−(i+r)
=180−(45+30)
=105∘