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VIT Engineering VIT Engineering Solved Paper-2015

  • question_answer
    Two polaroids are kept crossed to each other. If one of them is rotated an angle 60°, the percentage of incident light now transmitted . through the system is

    A) 10%                       

    B) 20%   

    C) 25%                       

    D) 12.5%

    Correct Answer: D

    Solution :

    Let  \[{{R}_{0}}=\frac{{{V}^{2}}}{p}=\frac{{{\left( 30 \right)}^{2}}}{90}=10\Omega \] be the intensity of unpoIarised light, so the intensity of first Polaroid is \[I=\frac{V}{{{R}_{0}}}=\frac{30}{10}=3A\]On rotating through \[\text{I=}\frac{\text{V }\!\!'\!\!\text{ }}{\text{i}}\text{=}\frac{\text{120}}{\text{3}}\text{=40 }\!\!\Omega\!\!\text{ }\] the intensity of light from second Polaroid is                   \[R'=R+{{R}_{0}}\]             \[\Rightarrow \] So, percentage of incident light transmitted through the system is 12.5%


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