Refraction of light through a prism

[logearav]

Homework Statement

Revered members,
Please see my attachment which deals with refraction of light through a prism. PQ is incident ray, QR is refracted ray and RS is emergent ray. i1,i2 are angles of incidence. i1 is angle of incidence, but how i2 qualifies to angle of incidence. Similarly how r2 is angle of refraction? Please help members

Homework Equations

The Attempt at a Solution

 

[grzz]

I am assuming a glass prism in air.
To put it exactly, (according to the direction the light is following) r2 is the angle at which the light is incident at the glass-air interface and i2 is the angle of refraction when the light passes form glass into air.
But, since the light could go exactly in the reversed path, i2 can be an angle of incidence of light on glass and then r2 would be the angle or refraction as light passes from air to glass.

 

[logearav]

Thanks for the reply grzz. Nice explanation.