RAJASTHAN ­ PET Rajasthan PET Solved Paper-2012

  • question_answer
    If an\[\alpha -\]particle of energy 10 MeV is deflected back when its distance from the nucleus is \[4\times {{10}^{-14}}m,\]then the atomic number of the atom is

    A)  129          

    B)  130

    C)  139          

    D)  120

    Correct Answer: C

    Solution :

     Given, \[E=10\text{ }MeV=10\times 1.6\times {{10}^{-13}}J\] \[=1.6\times {{10}^{-12}}J\] \[{{r}_{0}}=4\times {{10}^{-14}}m\] Using,    \[{{r}_{0}}=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{2Z{{e}^{2}}}{E}\] \[Z=\frac{({{r}_{0}}E)4\pi {{\varepsilon }_{0}}}{2({{e}^{2}})}\] \[=\frac{(4\times {{10}^{-14}})(1.6\times {{10}^{-12}})}{2\times {{(1.6\times {{10}^{-19}})}^{2}}}\times \frac{1}{9\times {{10}^{9}}}\] \[=139\]


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