question_answer

When a ray of light is incident normally on one refracting surface of an equilateral prism (Refractive index of the material of the prism = 1.5                                  [EAMCET (Med.) 2000]

A)            Emerging ray is deviated by 30o

B)            Emerging ray is deviated by 45o

C)            Emerging ray just grazes the second refracting surface      

D)            The ray undergoes total internal reflection at the second refracting surface

Correct Answer: D

Solution :

                   Critical angle for the material of prism \[C={{\sin }^{-1}}\left( \frac{1}{\mu } \right)={{\sin }^{-1}}={{42}^{o}}\] since angle of incidence at surface \[AB\ ({{60}^{o}})\] is greater then the critical angle \[({{42}^{o}})\] so total internal reflection takes place.