JEE Main & Advanced Physics Nuclear Physics And Radioactivity Question Bank Radioactivity

  • question_answer
    During mean life of a radioactive element, the fraction that disintegrates is                                          [CPMT 2001]

    A)            e    

    B)            \[\frac{1}{e}\]

    C)            \[\frac{e-1}{e}\]                 

    D)            \[\frac{e}{e-1}\]

    Correct Answer: C

    Solution :

                       By using \[N={{N}_{0}}{{e}^{-\lambda t}}\]and average life time \[t=\frac{1}{\lambda }\]                    So \[N={{N}_{0}}{{e}^{-\lambda \times 1/\lambda }}={{N}_{0}}{{e}^{-1}}\Rightarrow \frac{N}{{{N}_{0}}}={{e}^{-1}}=\frac{1}{e}\]            Now disintegrated fraction \[=1-\frac{N}{{{N}_{0}}}=1-\frac{1}{e}=\frac{e-1}{e}\]


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