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JEE Main & Advanced Physics Ray Optics Question Bank Photometry

  • question_answer
    The maximum illumination on a screen at a distance of 2 m from a lamp is 25 lux. The value of total luminous flux emitted by the lamp is                                                                     [JIMPER 1997]

    A)            1256 lumen                           

    B)            1600 lumen

    C)            100 candela                          

    D)            400 lumen

    Correct Answer: A

    Solution :

                       \[I=\frac{L}{{{r}^{2}}}\]\[\Rightarrow L=I.{{r}^{2}}\]\[=22\times {{2}^{2}}=100\]            Now \[\varphi =4\pi \,L=4\times 3.14\times 100\]= 1256 lumen.


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