If one face of a prism angle `30^(@)` and `mu=sqrt( 2)` is silvered, the incident ray retraces its initial path. What is the angle of incidence ?

Explanation

As incident ray retracess its path the ray is incident normally on the silvered face of the prism as shown in Figure .
Further as in `Delta AED 30^(@) + 90^(@) + /_ D = 180^(@)`
`rArr /_ D = 60^(@)`
Now as by construction `/_ D =+ /_r =90^(@)`
`rArr /_ r= 90^(@) - 60^(@) = 30^(@)`