A ray of light passes through four transparent media with refractive indices`mu_1`,`mu_2`,`mu_3` and `mu_4` as shown in the figure. The surfaces of all 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_(4) = mu_(1)`

Answer

D

Explanation

Applying Snell's law at B and C ,

`mu "sin"1 ` = constant or `mu_(1) "sin" I_(B)= mu_(4) "sin" i_(C)`
But `AB || CD therefore i_(B) = i_(C) "or" mu_(1) = mu_(4)`