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 ?

Options

A. `60^(@)`
B. `30^(@)`
C. `45^(@)`
D. `90^(@)`

Answer

C

Explanation

It is clear from the figure that the ray will retrace the path when the refracted ray QR is incident normally on the polished surface AC. Thus angle of refraction, r=`30^(@)`.
`mu=(sini)/(sinr)`,
`:.sini=musinr`
`sini=sqrt(2)xxsin30^(@)=sqrt(2)xx(1)/(2)=(1)/(sqrt(2))`
`:.i=45^(@)`