MGIMS WARDHA MGIMS WARDHA Solved Paper-2010

  • question_answer
    Number of nuclei of a radioactive substance at time t = 0 are 2000 and 1800 at time r = 2 s. Number of nuclei left after t = 6 s is

    A)  1442                                     

    B)  1554

    C)  1652                                     

    D)  1458

    Correct Answer: D

    Solution :

                     From      \[N={{N}_{0}}{{e}^{-\lambda t}}\] \[1800=2000{{e}^{-\lambda \times 2}}\] \[\frac{9}{10}={{e}^{-2\lambda }}\] \[{{e}^{-\lambda }}={{\left( \frac{9}{10} \right)}^{1/2}}\] Number of nuclei left after 6s, \[N={{N}_{0}}{{e}^{-\lambda t'}}\] \[=2000{{e}^{-\lambda \times 6}}\] \[=2000{{({{e}^{-\lambda }})}^{6}}\] \[=2000{{\left[ {{\left( \frac{9}{10} \right)}^{1/2}} \right]}^{6}}\] \[=2000{{\left( \frac{9}{10} \right)}^{3}}\] \[=2000\times \frac{729}{1000}\] \[=1458\]


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