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

  • question_answer
    Activity of radioactive element decreased to one third of original activity \[{{R}_{0}}\] in 9 years. After further 9 years, its activity will be                                                                    [DCE 2002]

    A)            \[{{R}_{0}}\]                         

    B)            \[\frac{2}{3}{{R}_{0}}\]

    C)            \[{{R}_{0}}/9\]                     

    D)            \[{{R}_{0}}/6\]

    Correct Answer: C

    Solution :

                       Activity \[R={{R}_{0}}{{e}^{-\lambda t}}\]                    \[\frac{{{R}_{0}}}{3}={{R}_{0}}{{e}^{-\lambda \times 9}}\Rightarrow {{e}^{-9\lambda }}=\frac{1}{3}\]                   ...(i)                    After further 9 years \[{R}'=R\,{{e}^{-\lambda t}}=\frac{{{R}_{0}}}{3}\times {{e}^{-\lambda \times 9}}\]              ...(ii)                    From equation (i) and (ii) \[{R}'=\frac{{{R}_{0}}}{9}\].


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