JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2012

  • 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 \[\mu =\frac{\sin i}{\sin r}\]                        ?.(i) 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. (i), 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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