J & K CET Engineering J and K - CET Engineering Solved Paper-2007

  • question_answer
    How many photons are emitted by a laser source of \[5\times {{10}^{-3}}W\]operating at \[632.2\text{ }nm\]in \[2s\]?

    A)  \[3.2\times {{10}^{16}}\]    

    B)  \[1.6\times {{10}^{16}}\]

    C)  \[4\times {{10}^{16}}\]     

    D)  None of these

    Correct Answer: A

    Solution :

    Energy of each photon \[{{E}_{0}}=\frac{hc}{\lambda }\] \[=\frac{6.63\times {{10}^{-34}}\times 3\times {{10}^{8}}}{632.2\times {{10}^{-9}}}\] \[=3.15\times {{10}^{-19}}J\] Total energy  \[=E=Pt\] \[\therefore \] \[n{{E}_{0}}=Pt\] \[\Rightarrow \] \[n=\frac{Pt}{{{E}_{o}}}\] \[=\frac{5\times {{10}^{-3}}\times 2}{3.15\times {{10}^{-19}}}\] \[=3.2\times {{10}^{16}}\]


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