As shown in the diagram, when the incident ray is parallel to base of the prism, the emergent ray grazes along the second surface.
If refractive index of the material of prism is 2, the angle θ of prism is: [2026]
(4)
For grazing emergence
sinr2=1μ
By Snell's Law at incident surface
1×12=2sinr1
r1=30°
r1+r2=A
A=75°
75°+45°+θ=180°
θ=60°