Haryana PMT Haryana PMT Solved Paper-2008

  • question_answer
    The momentum of a photon of energy 1 MeV   in kg-m/s, will be

    A)  \[0.33\times {{10}^{6}}\]                            

    B)  \[7\times {{10}^{-24}}\]

    C)  \[{{10}^{-22}}\]                               

    D)  \[5\times {{10}^{-22}}\]

    Correct Answer: D

    Solution :

                    Energy of photon is given by \[E=\frac{hc}{\lambda }\]             ??(i) where h is Plancks constant, c the velocity of light and \[\lambda \] its wavelength. de-Broglie wavelength is given by                 \[\lambda =\frac{h}{p}\]                              ??.(ii) p being momentum of photon. From Eqs. (i) and (ii), we can have                 \[E=\frac{hc}{h/p}=pc\] or              \[p=E/c\] Given, \[E=1MeV=1\times {{10}^{6}}\times 1.6\times {{10}^{-19}}J\]                 \[c=3\times {{10}^{8}}m/s\] Hence, after putting numerical values, we obtain \[p=\frac{1\times {{10}^{6}}\times 1.6\times {{10}^{-19}}}{3\times {{10}^{8}}}kg-m/s\] \[=5\times {{10}^{-22}}kg-m/s\]


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