A ray of light incident at `60^(@)` on a prism undergoes a deviation of `20^(@)`. If the angle of the prism is 40, S.T. the emergent ray is normal to the second face of the prism.

Explanation

`d=(i_(1)+i_(2))-A`
`20^(2)=60^(@)+i_(2)-40^(@)`
`therefore i_(2)-0`.
Hence, emergent ray is normal to the face of the prism.