JCECE Engineering JCECE Engineering Solved Paper-2013

  • question_answer
    An unpolarized beam of light is incident on a group of four polarizing sheets, which are arranged in such a way that the characteristic direction of each polarizing sheet makes an angle of \[{{30}^{o}}\] with that of the preceding sheet. The fraction of incident unpolarized light transmitted is

    A) \[\frac{27}{128}\]                                            

    B) \[\frac{128}{27}\]

    C)  \[\frac{37}{128}\]                                           

    D)  \[\frac{128}{37}\]

    Correct Answer: A

    Solution :

    Let \[{{I}_{0}}\] be the intensity of unpolarized light, then intensity of light transmitted From 1st  polarizing sheets\[=\frac{{{I}_{0}}}{2}\] From 2nd polarizing sheet,        \[I'=\frac{{{I}_{0}}}{2}(\cos {{30}^{o}})=\frac{{{I}_{0}}}{2}{{\left( \frac{\sqrt{3}}{2} \right)}^{2}}=\frac{{{I}_{0}}}{2}\left( \frac{3}{4} \right)\] From 3rd polarizing sheet,       \[I''=I'{{(\cos {{30}^{o}})}^{2}}=\frac{{{I}_{0}}}{2}\left( \frac{3}{4} \right){{\left( \frac{\sqrt{3}}{2} \right)}^{2}}=\frac{{{I}_{0}}}{2}{{\left( \frac{3}{4} \right)}^{2}}\] From 4th polarizing sheet,  \[I'''=I''(cos{{30}^{o}})=\frac{{{I}_{0}}}{2}{{\left( \frac{3}{4} \right)}^{2}}={{\left( \frac{\sqrt{3}}{2} \right)}^{2}}={{I}_{0}}\times \frac{27}{128}\] \[\therefore \]  \[\frac{I'''}{{{I}_{0}}}=\frac{27}{128}\]


You need to login to perform this action.
You will be redirected in 3 sec spinner