A laser beam enters a stack of three transparent layers—air
PHYSICS · Single correct · CBSE · Physics · Light — Reflection and Refraction · Light — Reflection and Refraction
Problem
A laser beam enters a stack of three transparent layers—air, a plastic slab, and water—at an angle of 35∘ with respect to the normal to the surfaces. The plastic slab’s two faces are parallel to each other, and the water surface is also parallel to those faces. After emerging into the water, the beam is observed to travel in a direction parallel to its original path in air. Which of the following statements best explains this observation?
(a) Because the faces of the plastic slab are parallel, the light crosses each interface at normal incidence, so it never bends as it passes through.
(b) Air and water have almost identical indices of refraction, so the ray emerges in water with the same direction it had in air.
(c) The ray refracts at each interface, but since the surfaces are parallel, the second refraction reverses the first, leaving the ray’s final direction parallel to its initial direction.
(d) Multiple total internal reflections within the plastic slab redirect the beam until it exits along the same line it entered.