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JEE Main & Advanced JEE Main Online Paper (Held on 9 April 2013)

  • question_answer
                                    Light is incident from a medium into air at two possible angles of incidence (a) \[{{20}^{0}}\] and (b)\[{{40}^{0}}\] In the medium light travels 3.0 cm in 0.2ns. The ray will :                   JEE Main Online Paper (Held On 09 April 2013)

    A)                 suffer total internal reflection in both cases (a) and (b)                

    B)                 suffer total internal reflection in cases (b) only                

    C)                 have partial reflection and partial transmission in case (b)                

    D)                 have 100% transmission in case (a)                

    Correct Answer: A

    Solution :

                    Refractive index                 \[=\mu =\frac{c}{v}=\frac{3\times {{10}^{8}}}{3\times {{10}^{-2}}/0.2\times {{10}^{-9}}}\]                 \[=\frac{{{10}^{8}}\times 0.2\times {{10}^{-9}}}{{{10}^{-2}}}=2\]                 From total internal reflection \[=\sin \,{{i}_{C}}=\frac{1}{\mu }=\frac{1}{2}\]                 So, \[{{i}_{C}}={{30}^{0}}\]                 For total internal reflection \[i>{{i}_{c}}\]                 So for second case, total internal reflection is possible.                 


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