question_answer

A light ray travels from medium 1 of refractive index \[{{\mu }_{1}}\] to medium 2 of refractive index \[{{\mu }_{2}}\], where \[{{\mu }_{2}}<{{\mu }_{1}}\] Write an expression for critical angle of incidence.  

Answer:

                 As shown in Fig. when \[i={{i}_{c}},r={{90}^{\circ }}\] Using Snell?s law of refraction, \[{{\mu }_{1}}\sin {{i}_{c}}={{\mu }_{2}}\sin {{90}^{\circ }}\] or \[\sin {{i}_{c}}=\frac{{{\mu }_{2}}}{{{\mu }_{1}}}\] or \[{{i}_{c}}={{\sin }^{-1}}\left( \frac{{{\mu }_{2}}}{{{\mu }_{1}}} \right)\]