JCECE Engineering JCECE Engineering Solved Paper-2008

  • question_answer
    Monochromatic light of frequency \[6.0\times {{10}^{14}}Hz\]  is produced by a laser. The power emitted is\[2\times {{10}^{-3}}W\]. The number of photons emitted, on the average, by the source per second is

    A) \[5\times {{10}^{15}}\]                 

    B) \[5\times {{10}^{16}}\]

    C) \[5\times {{10}^{17}}\]                 

    D)  \[5\times {{10}^{14}}\]

    Correct Answer: A

    Solution :

    Key Idea Photons are the packets of energy. Power emitted,                 \[P=2\times {{10}^{-3}}W\] Energy of photon,                 \[E=hv=6.6\times {{10}^{-34}}\times 6\times {{10}^{14}}J\] where \[h\] being Planck's constant. Number of photons emitted per second                 \[n=\frac{P}{E}\]                    \[=\frac{2\times {{10}^{-3}}}{6.6\times {{10}^{-34}}\times 6\times {{10}^{14}}}=5\times {{10}^{15}}\]


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