When a light beam traveling in medium 1 with index of refraction reaches a flat…
PHYSICS · Multi-part · CBSE · Physics · Ray Optics and Optical Instruments · Ray Optics and Optical Instruments
Problem
When a light beam traveling in medium 1 with index of refraction n1 reaches a flat interface to medium 2 with index n2 (n1>n2), observers notice that for sufficiently oblique incidence the beam does not emerge into medium 2 but is instead reflected back into medium 1.
Answer the following questions about this phenomenon in essay form. Support your reasoning with clear verbal argumentation and any algebraic relations you judge necessary. Do not perform numerical calculations.
(a) Describe the physical conditions that must be satisfied at the interface for the reflected intensity to reach 100 %. In your answer, refer explicitly to the directions of the refracted and reflected rays with respect to the normal.
(b) Show how one can obtain a limiting angle θc (called the critical angle) that separates partial transmission from complete reflection. Express sinθc in terms of n1 and n2, stating all assumptions you make.
(c) Using your result from part (b), explain qualitatively why a light ray traveling from water into glass can never meet the condition in part (a), no matter what the angle of incidence from the water side is.