NEET Physics Photo Electric Effect, X- Rays & Matter Waves NEET PYQ-Photo Electric Effect,X-Rays

  • question_answer
    The momentum of a photon of energy 1 MeV in kg m/s, will be:                        [AIPMT (S) 2006]

    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 \[\lambda \] 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,  \[E=1\text{ }MeV=1\times {{10}^{6}}\times 1.6\times {{10}^{-19}}\,J\]
    \[c=3\times {{10}^{8}}\,m/s\,\]
    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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