NEET Sample Paper NEET Sample Test Paper-86

  • question_answer
    A prism of refractive index 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 :

    [a]  \[\mu =\frac{\sin \frac{{{\delta }_{m}}+A}{2}}{\sin \frac{A}{2}}\] \[\Rightarrow \] \[\sqrt{2}=\frac{\sin \frac{{{\delta }_{m}}+60}{2}}{\sin \,30{}^\circ }\] \[\sin \frac{{{\delta }_{m}}+60}{2}=\sqrt{2}\times \frac{1}{2}=\frac{1}{\sqrt{2}}=\sin \,45{}^\circ \] \[\frac{{{\delta }_{m}}+60}{2}=45{}^\circ \] \[\Rightarrow \]\[{{\delta }_{m}}+60=90{}^\circ ;\] \[{{\delta }_{m}}=30{}^\circ \] Now \[{{\delta }_{m}}=2i-A\] \[\Rightarrow \] \[i=\frac{{{\delta }_{m}}+A}{2}=\frac{30+60}{2}45{}^\circ \]


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