NEET AIPMT SOLVED PAPER SCREENING 2006

  • 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 Planck?s constant, c the velocity of light and  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 = 1 MeV = \[1\times {{10}^{6}}\times 1.6\times {{10}^{-19}}\,J\]                 \[c=3\times {{10}^{8}}\,m/s\,\]                 Hence, after putting numerical values, we obtain                 \[p=\frac{1\times {{10}^{6}}\times 1.6\times {{10}^{-19}}}{3\times {{10}^{8}}}\,kgm/s\]                 \[=5\times {{10}^{-22}}\,kgm/s\]


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