NEET Sample Paper NEET Sample Test Paper-50

  • question_answer 26) The photo sensitive surface is receiving light of wavelength \[5000\text{ }\overset{\text{o}}{\mathop{\text{A}}}\,\] at the rate of \[{{10}^{-8}}\text{ }J/s\]. The number of photons received per second is:

    A) \[2.5\times {{10}^{10}}\]                     

    B) \[2.5\times {{10}^{11}}\]

    C) \[2.5\,\,\times \,\,{{10}^{12}}\]             

    D) \[2.5\,\,\times \,\,{{10}^{9}}\]

    Correct Answer: A

    Solution :

    \[\lambda \,\,=\,\,5000\,\overset{{}^\circ }{\mathop{A}}\,\] Energy received per second \[=\,\,{{10}^{-}}^{\,8}J/sec\] \[\therefore \] Energy of one photon is \[E=hv=hc/\lambda \], \[=\,\,\frac{6.63\times {{10}^{-34}}\times 3\times {{10}^{8}}}{5000\times {{10}^{-10}}}\,\,=\,\,3.99\times {{10}^{-19}}J\]    \[\therefore \] Number of photon received per second \[=\frac{Energy\text{ }received\text{ }per\text{ }second}{Energy\text{ }of\text{ }one\text{ }photon}\] \[=\,\,\frac{{{10}^{-8}}}{3.99\text{ }\times {{10}^{-}}^{19}}\,\,=\,\,2.5\times {{10}^{10}}\]

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