Manipal Engineering Manipal Engineering Solved Paper-2009

  • question_answer
    In a radioactive disintegration, the ratio of initial number of atoms of the number of atoms present at an instant of time equal to its mean life is

    A)  \[\frac{1}{{{e}^{2}}}\]                                  

    B)  \[\frac{1}{e}\]

    C)  e                           

    D)        \[{{e}^{2}}\]

    Correct Answer: C

    Solution :

    Let the initial number of atoms at time\[t=0\]be\[{{N}_{0}}\]. Let\[N\]be the number of atoms at any instant\[t.\] Mean life\[\tau =\frac{1}{\lambda }\], where\[\lambda \]is disintegration constant. Given,\[t=\tau \] According to radioactive disintegration law,                 \[N={{N}_{0}}{{e}^{-\lambda t}}\] or            \[N={{N}_{0}}{{e}^{-\lambda \times \frac{1}{\lambda }}}=\frac{{{N}_{0}}}{e}\] or            \[\frac{{{N}_{0}}}{N}=e\]


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