Question

“A ray of light incident on a rectangular glass slab immersed in any medium emerges parallel to itself”. Draw labeled ray diagrams to justify the statement.

Answer 1

- Hint:When a ray of light enters the medium having higher refractive index, it bends towards the normal and when emerges out to the same medium as before, it gets refracted away from the normal.

Complete step-by-step solution -

Suppose a ray of light travelling in air passes through a medium having higher density, here, rectangular glass slab PQSR and different refractive index incident with an angle of incidence ‘i’ at point ‘O’, and then refracts at an angle ‘r’ towards the normal and travels through glass slab and emerge out through it and refracts away from the normal at an angle of emergence ‘e’.
When ray enters the glass medium, it bends towards the normal making an angle of refraction ‘r’, and then travels through the glass medium.

The ray after travelling in the medium, emerges from it at an angle of emergence ‘e’, which is equal to the angle of incidence and therefore, emerges parallel to the incident ray as shown in the figure. Had there been no medium, the light would have taken the path that is shown by the lighter line which is parallel to the emerging ray after travelling in the medium.

Note- Pictorial representation would be more helpful in understanding this concept, and it should be memorized that whenever light ray travels from a medium of low refractive index to a medium of higher refractive index, it bends towards the normal and vice versa when travels from a medium of higher refractive index to a medium of lower refractive index.