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JEE Main & Advanced JEE Main Paper (Held on 10-4-2019 Afternoon)

  • question_answer
    A 2 mW laser operates at a wavelength of 500 nm. The number of photons that will be emitted per second is :
    [Given Planck's constant \[h=6.6\times {{10}^{34}}Js,\] speed of light \[c=3.0\times {{10}^{8}}m/s\]]
    [JEE Main 10-4-2019 Afternoon]

    A) \[2\times {{10}^{16}}\]                   

    B) \[1.5\times {{10}^{16}}\]

    C) \[5\times {{10}^{15}}\]       

    D) \[1\times {{10}^{16}}\]

    Correct Answer: C

    Solution :

                \[P=\frac{n.hc}{\lambda }\]           \[n=\frac{P\lambda }{h.c}\]        \[=\frac{2\times {{10}^{-3}}\times 500\times {{10}^{-9}}}{6.6\times {{10}^{-34}}\times 3\times {{10}^{8}}}\]\[=1.5\times {{10}^{16}}\]


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