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KVPY Sample Paper KVPY Stream-SX Model Paper-4

  • question_answer
    Two Polaroid?s are placed in the path of unpolarized beam of intensity \[{{I}_{0}}\] such that no light is emitted from the second Polaroid. If a third polaroid whose polarization axis makes an angle \[\theta \] with the polarization axis of first polaroid, is placed between these polaroid then the  intensity of light emerging from the last polaroid will be                                   

    A) \[\left( \frac{{{I}_{0}}}{8} \right){{\sin }^{2}}2\theta \] 

    B) \[\left( \frac{{{I}_{0}}}{4} \right){{\sin }^{2}}2\theta \]

    C) \[\left( \frac{{{I}_{0}}}{2} \right){{\cos }^{4}}\theta \]              

    D) \[{{I}_{0}}{{\cos }^{4}}\theta \]

    Correct Answer: A

    Solution :

    [a] \[I=\left[ \left( \frac{{{I}_{0}}}{2} \right){{\cos }^{2}}\theta  \right]{{\cos }^{2}}\left( 90{}^\circ -\theta  \right)\] \[=\frac{{{I}_{0}}}{2}{{\cos }^{2}}\theta {{\sin }^{2}}\theta \] \[=\frac{{{I}_{0}}}{8}{{\sin }^{2}}2\theta \]  


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