CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2007

  • question_answer
    When the angle of incidence is \[{{60}^{o}}\] on the surface of a glass slab, it is found that the reflected ray is completely polarised. The velocity of light in glass is

    A)  \[\sqrt{2}\times {{10}^{8}}m{{s}^{-1}}\]              

    B)  \[\sqrt{3}\times {{10}^{8}}m{{s}^{-1}}\]

    C)  \[2\times {{10}^{8}}m{{s}^{-1}}\]                            

    D)  \[3\times {{10}^{8}}m{{s}^{-1}}\]

    Correct Answer: B

    Solution :

    Refractive index of glass, \[{{\mu }_{g}}=\tan {{\theta }_{P}}\] where \[{{\theta }_{P}}=\] polarising angle \[\Rightarrow \]               \[{{\mu }_{g}}=\tan {{60}^{o}}=\sqrt{3}\] Now,     \[{{\mu }_{g}}=\frac{c}{{{v}_{g}}}\] \[\therefore \]  \[\frac{c}{{{v}_{g}}}=\sqrt{3}\] \[\Rightarrow \]               \[{{v}_{g}}=\frac{3\times {{10}^{8}}}{\sqrt{3}}\]                 \[=\sqrt{3}\times {{10}^{8}}\]


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