NEET Sample Paper NEET Sample Test Paper-57

  • question_answer
    If a ray of light in a denser medium strikes a rarer medium at an angle of incidence i, the angle of reflection and refraction are respectively r and r'. If the reflected and refraction rays are at right angles to each other, the critical angle for the given pair of media is:

    A) \[si{{n}^{-1}}1\text{ (tan r }\!\!'\!\!\text{ )}\]      

    B) \[si{{n}^{-1}}1\text{ (tan r }\!\!'\!\!\text{ )}\]

    C) \[{{\tan }^{-1}}1\text{ (Sin i }\!\!'\!\!\text{ )}\]   

    D) \[Co{{t}^{-1}}1\text{ (tan i }\!\!'\!\!\text{ )}\]

    Correct Answer: B

    Solution :

    [b]   \[\frac{1}{\mu }=\frac{\sin \,i}{Sin\,{{r}^{11}}}.....(1)\] \[r+{{r}^{1}}=90\] \[{{r}^{1}}=90-r\] \[sin\text{ }{{r}^{1}}=\text{ }\sin \,(90-r)=\text{ }cos\text{ }r\text{ }or\text{ }cos\text{ }i\] Put this value in (1) \[\frac{1}{\mu }=\frac{Sin\,i}{Cos\,r}=\frac{Sin\,i}{Cos\,i}=\tan \,i\] \[\sin \,{{i}_{c}}\,\tan \,i=\tan \,r\] \[{{i}_{c}}={{\sin }^{-1}}\,=[\tan \,r]\]


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