NEET Sample Paper NEET Sample Test Paper-21

  • question_answer
    A \[\gamma -\]ray photon produces an electron-positron pair, each moving with a K.E of 0.01 MeV The energy of the\[\gamma -\]ray photon is

    A)  1.02 MeV                   

    B)  1.04 MeV       

    C)    2.08 MeV        

    D)  1.03 MeV

    Correct Answer: B

    Solution :

    Rest mass energy of an electron \[={{m}_{0}}{{C}^{2}}=(9.1\times {{10}^{-11}})\times {{(3\times {{10}^{8}})}^{2}}J\] \[=\frac{(9.1\times {{10}^{-31}})\times {{(3\times {{10}^{8}})}^{2}}}{1.6\times {{10}^{-13}}}\text{MeV}\] The total energy of an electron \[=E={{m}_{0}}{{C}^{2}}+kE\] \[\therefore \]Total energy of two electrons \[=2{{m}_{0}}{{C}^{2}}+2kE\] \[\therefore \]Energy of incident \[\gamma -\]ray photon             \[=(2\times 0.51+2\times 0.01)\,MeV=1.04\,\text{MeV}\] Hence, the correction option is (b).

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