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  • question_answer
    A ray is incident at an angle of incidence i on one surface of a small angle prism (with angle of prism A) and emerges normally from the opposite surface. If the refractive index of the material of the prism is \[\mu \], then the angle of incidence is nearly equal to:                                                                                                                    [NEET 2020]

    A)  \[\frac{2A}{\mu }\]                  

    B)       \[\mu A\]

    C)  \[\frac{\mu A}{2}\]                  

    D)       \[\frac{A}{2\mu }\]      

    Correct Answer: B

    Solution :

    [b] Light ray emerges normally from another surface, hence, e(angle of emergence) = 0
    \[{{r}_{2}}=0\]
    \[{{r}_{1}}+{{r}_{2}}=A\]
    \[\Rightarrow {{r}_{1}}=A\]
    Applying Snell's law on first surface
    \[1.sin\,i=\mu \,sin\,\,{{r}_{1}}\]
    \[\Rightarrow \sin i=\mu \sin \,A\]
    For small angles \[(sin\,\theta \approx \theta )\]
    hence \[i=\text{ }\mu A\]


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