Uttarakhand PMT Uttarakhand PMT Solved Paper-2006

  • question_answer
    A prism of refractive index \[\sqrt{2}\] has a refracting angle of\[60{}^\circ \]. At what angle a ray must be incident on it, so that it suffers a minimum deviation :

    A)  \[45{}^\circ \]              

    B)  \[60{}^\circ \]

    C)  \[90{}^\circ \]              

    D)  \[180{}^\circ \]

    Correct Answer: A

    Solution :

     The relation for refractive index of prism is \[\mu =\frac{\sin i}{\sin r}\]            ...(1) The condition for minimum deviation is \[r=\frac{A}{2}=\frac{60{}^\circ }{2}=30{}^\circ \] Putting the given value of\[\mu =\sqrt{2}\]and\[r=30{}^\circ \]in Eq. (1), we get \[\sqrt{2}=\frac{\sin i}{\sin 30{}^\circ }\] So,        \[\sin i=\sqrt{2}\times \frac{1}{2}=\frac{1}{\sqrt{2}}\] \[\sin i=\sin 45{}^\circ \] \[i=45{}^\circ \]


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