JCECE Engineering JCECE Engineering Solved Paper-2011

  • question_answer
    Let \[T\] be the mean life of a radioactive sample. \[75%\] of the active nuclei present in the sample initially will decay in time

    A) \[2T\]                                   

    B) \[\frac{1}{2}(\ln 2)T\]

    C)  \[4T\]                                  

    D)  \[2(\ln 2)T\]

    Correct Answer: D

    Solution :

    As\[\frac{N}{{{N}_{0}}}={{e}^{-\lambda t}}\]                 \[\frac{25}{100}={{e}^{-\lambda t}}=\frac{1}{4}\] or            \[-\lambda t{{\log }_{e}}e=-{{\log }_{e}}4=-2{{\log }_{e}}2\]                 \[t=\frac{2{{\log }_{e}}2}{\lambda }\] Because mean life\[T=\frac{1}{\lambda }\]                 \[t=(2\ln 2)T\]


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