Question

A ray of light passes through four transparent media with refractive indices ${\mu }_1,{\mu }_2,{\mu }_3$ & ${\mu }_4$ 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:

• A. ${\mu }_1={\mu }_2$
• B. ${\mu }_2={\mu }_3$
• C. ${\mu }_3={\mu }_4$
• D. ${\mu }_4={\mu }_1$

Answer 1

The correct option is D ${\mu }_4={\mu }_1$

Since, the light undergoes refraction from 3 transparent media, its speed and trajectory will only depend on the refractive indices of the respective medium.
Since, the direction of the ray of light is same in the first and the fourth medium, the refractive indices of the 2 media have to be the same.
So, ${\mu }_1={\mu }_4$