The refractive index of the material of a prism is `sqrt(2)` and the angle of the prism is `30^(@)`. One of the two refracting surfaces of the prism is made a mirror inwards, by silver coating. A beam of monochromatic light entering the prism from the other face will retrace its path (after reflection from the silvered surface) if its angle of incidence on the prism is

Options

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

Answer

B

Explanation

To retrace its path after reflection, light ray should fall perpendicular to mirror face of prism : hence angle of refraction at other face must be `30^(@)` as shown in figure.

`(sini)/(sin30^(@))=(sqrt2)/(1)`
`rArr" "sini=sqrt2xx(1)/(2)`
`sini=(1)/(sqrt2)" i.e. "i=45^(@)`
Hence option (b) is correct.