Copy the diagram given below and complete the path of light ray till it emerges out of the prism. The critical angle of glass is $42^o$. In your diagram mark the angles wherever necessary.

The diagram is shown. The ray $PQ$ enters the prism from the side $AB$, its angle of incidence is $0°$. Thus it does not undergo any refraction. Its angle of refraction is also $0°$. When this light ray reaches the base of the prism (BC), its angle of incidence (on the boundary $BC$) is $60°$ which is more than its critical angle ($42°$). Thus this incident light ray ($QR$) does not enter into the next medium, instead it undergoes total internal reflection. When this reflected light ray ($RS$) reaches the side $AC$, its angle of incidence is $0°$. Again, it does not undergo any refraction, which causes the angle of emergence to become $0°$.