Question

A prism having refractive index `sqrt2` and refractive angle `30^@` has one of the refractive surfaces polished. A beam of light incident on the other surfaces will trace its path if the angle of incidence is
A. `0^@`
B. `30^@`
C. `45^@`
D. `60^@`

Answer 1

Correct Answer - C
If beam retraces its path, for this, ray must be incident normally on silvered surface.

`1xxsini=musin30^@`
`sini=sqrt2xx1//2=1/sqrt2=sin45^@`
`i=45^@`