A ray of light passes through four transparent media with refractive indices `mu_(1),mu_(2),mu_(3)andmu_(4)` as shown in the figure. The surface of are media are parallel. If the emergent ray CD is parallel to the incident ray AB , we must have

Options

A. `mu_(1)=mu_(2)`
B. `mu_(2)=mu_(3)`
C. `mu_(3)=mu_(4)`
D. `mu_(1)=mu_(4)`

Answer

D

Explanation

Given : Refractive indices of transparent media `=mu_(1),mu_(2),mu_(3),mu_(4)` and emergent ray CD parallel to the incident ray AB .
We know from the snell's law that `mu` sin i = constant
Applying this law at point B and C , we get `mu_(1) sin i_(B) = mu_(4) sin i_(c)`
Since AB is parallel to CD therefore `i_(B) = i_(C)`