Haryana PMT Haryana PMT Solved Paper-2000

  • question_answer
    When a ray of light is refracted from one medium into another medium. The wave length changes from \[4000\overset{\text{o}}{\mathop{\text{A}}}\,\] to \[6000\overset{\text{o}}{\mathop{\text{A}}}\,\]. The critical angle for a ray from second medium to first medium will be :

    A)  \[{{\sin }^{-1}}\left( \frac{2}{\sqrt{13}} \right)\]                               

    B) \[{{\tan }^{-1}}\left( \frac{3}{2} \right)\]

    C) \[{{\cos }^{-1}}\left( \frac{1}{7} \right)\]                               

    D) \[{{\sin }^{-1}}\left( \frac{2}{3} \right)\]

    Correct Answer: D

    Solution :

                    Using the relation \[\frac{\sin i}{\sin r}=\frac{{{\mu }_{2}}}{{{\mu }_{1}}}=\frac{{{\lambda }_{1}}}{{{\lambda }_{2}}}=\frac{4000\overset{\text{o}}{\mathop{\text{A}}}\,}{6000\overset{\text{o}}{\mathop{\text{A}}}\,}=\frac{2}{3}\]                 So,          \[Sin\,\,C=\frac{{{\mu }_{rarer}}}{{{\mu }_{denser}}}=\frac{{{\mu }_{2}}}{{{\mu }_{1}}}=\frac{2}{3}\]                 So,          \[C={{\sin }^{-1}}\left( \frac{2}{3} \right)\]


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