JEE Main & Advanced Physics Ray Optics Question Bank Total Internal Reflection

  • question_answer
    A ray of light is incident at an angle i from denser to rare medium. The reflected and the refracted rays are mutually perpendicular. The angle of reflection and the angle of refraction are respectively r and r' , then the critical angle will be                         [IIT-JEE 1983; MP PET 1995;  CBSE PMT 1996; MP PMT 1985, 99; Pb. PET 2002]

    A) \[{{\sin }^{-1}}(\sin \,r)\]

    B) \[{{\sin }^{-1}}\,(\tan r')\]

    C) \[{{\sin }^{-1}}\,(\tan i)\]

    D) \[{{\tan }^{-1}}(\sin i)\]

    Correct Answer: C

    Solution :

    \[_{D}{{\mu }_{R}}=\frac{\sin i}{\sin {r}'}{{\Rightarrow }_{R}}{{\mu }_{D}}=\frac{\sin {r}'}{\sin \ i}=\frac{1}{\sin C}\]                    \[\Rightarrow \sin C=\frac{\sin i}{\sin (90-r)}=\frac{\sin i}{\cos r}=\frac{\sin i}{\cos i}\]  (as Ði = Ðr)            \[\Rightarrow \sin C=\tan i\Rightarrow C={{\sin }^{-1}}(\tan i)\]


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