A narrow laser beam in air (index of refraction ) is directed toward a rectangular…
PHYSICS · Multi-part · CBSE · Physics · Light — Reflection and Refraction · Light — Reflection and Refraction
Problem
A narrow laser beam in air (index of refraction 1.000) is directed toward a rectangular block of plexiglass (index 1.49). The incident beam arrives at the flat surface of the block at an angle of 28∘ measured relative to the surface of the block (that is, 28∘ above the plane of the face).
Answer the following, showing all reasoning, unit checks, and clearly labeling each intermediate quantity you introduce.
(a) Convert the given 28∘ surface–referenced angle to the corresponding angle measured from the normal to the surface.
(b) Determine the angle that the beam makes with the normal while inside the plexiglass block.
(c) State whether the beam bends toward or away from the normal upon entering the plexiglass, and justify your answer on the basis of the calculated angles.
(d) The laser exits the opposite face of the block into air, making the same angle with the normal that you obtained in part (a). Explain in 1–2 sentences why the emerging angle equals the original incident angle even though the light passed through a medium of higher index.