Light traveling trhought three transparent substances follows the path shown in figure. Arrange the indices of refraction in order from smallest to largest. Not the total internal reflection does occur on the bottom surface of medium 2.

Options

A. `n_(1) lt n_(2) lt n_(3)`
B. `n_(2) lt n_(1) lt n_(3)`
C. `n_(1) lt n_(3) lt n_(2)`
D. `n_(3) lt n_(1) lt n_(2)`

Answer

D

Explanation

As the ray moves toward the normal while entering medium 2 from 1, we have `n_(2) gt n_(1)`
For total internal reflection at interface of 2 and 3, `n_(2) gt n_(3)`.
Besides `n_(3)` should also be less than `n_(1)` or else ray would have emerged in medium 3, parallel to its parth in medium 1.
Hence, `n_(3) lt n_(1) lt n_(2)` is the correct order.