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JEE Main & Advanced Physics Question Bank Human Eye and Lens Camera

  • question_answer
    The exposure time of a camera lens at the \[\frac{f}{2.8}\] setting is \[\frac{1}{200}\] second. The correct time of exposure at \[\frac{f}{5.6}\] is [DCE 2003]

    A)            0.4 sec                                     

    B)            0.02 sec

    C)            0.002 sec                                

    D)            0.04 sec

    Correct Answer: B

    Solution :

                       Time of exposure \[\propto {{(f.\,number)}^{2}}\] \[\Rightarrow \frac{{{t}_{2}}}{{{t}_{1}}}={{\left( \frac{5.6}{2.8} \right)}^{2}}=4\]            \[{{t}_{2}}=4\,{{t}_{1}}=4\times \frac{1}{200}=\frac{1}{50}\]sec      = 0.02 sec.


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