question_answer

A triangular prism of glass is inside water. A ray, incident normally, on one of the faces, is totally reflected from face BC. Then the minimum refractive index of glass is -

A) \[\frac{\sqrt{3}}{2}\]     

B) \[\frac{5}{3}\]

C) \[\frac{2\sqrt{2}}{5}\]

D) \[\frac{4\sqrt{2}}{3}\]

Correct Answer: D

Solution :

[d] For T.I.R. \[45{}^\circ >C\] \[\therefore \sin 45{}^\circ >\operatorname{sinC}\] \[\therefore \frac{1}{\sqrt{2}}>\frac{4/3}{n}\] \[\therefore n>\frac{4\sqrt{2}}{3}\]