NEET Physics Ray Optics NEET PYQ-Ray Optics

  • question_answer
    The refractive index of the material of the prism is \[\sqrt{3},\] then the angle of minimum deviation of the prism is :                             [AIPMT 1999]

    A)              \[{{30}^{o}}\]           

    B)                   \[{{45}^{o}}\]

    C)              \[{{60}^{o}}\]           

    D)                   \[{{75}^{o}}\]

    Correct Answer: C

    Solution :

    The refractive index of material of prism (from Snell's law) is
                            \[\mu =\frac{\sin i}{\sin r}\]
                Here,     \[i=\frac{A+{{\delta }_{m}}}{2}\] and  \[r=\frac{A}{2}\]
                where A is the angle of prism and \[{{\delta }_{m}}\] the angle  of minimum deviation.
                Hence,  \[\mu =\frac{\sin \left( \frac{A+{{\delta }_{m}}}{2} \right)}{\sin \frac{A}{2}}\]
                Given, \[\mu =\sqrt{3},\] \[A={{60}^{o}}\] (for prism)
                Thus,    \[\sqrt{3}=\frac{\sin \left( \frac{60+{{\delta }_{m}}}{2} \right)}{\sin {{30}^{o}}}\]
                or         \[\sin \left( \frac{60+{{\delta }_{m}}}{2} \right)=\frac{1}{2}\times \sqrt{3}\]
                or         \[\sin \left( \frac{60+{{\delta }_{m}}}{2} \right)=\sin {{60}^{o}}\]
    or         \[\frac{60+{{\delta }_{m}}}{2}=60\]
    or         \[{{\delta }_{m}}=2\times 60-60={{60}^{o}}\]


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