NEET Sample Paper NEET Sample Test Paper-17

  • question_answer
    Two radioactive materials X and X have decay constants 10/1 and A., respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of \[{{X}_{1}}\]to that of \[{{X}_{2}}\]will be \[1/e\] after a time

    A) \[\frac{1}{(10\lambda )}\]     

    B)   \[\frac{1}{(11\lambda )}\]                 

    C) \[\frac{11}{(10\lambda )}\]

    D)               \[\frac{1}{(9\lambda )}\]   

    Correct Answer: D

    Solution :

    \[{{N}_{1}}={{N}_{0}}{{e}^{-10\lambda t}}\]and \[{{N}_{2}}={{N}_{0}}{{e}^{-\lambda t}}\] \[\therefore \]    \[\frac{{{N}_{1}}}{{{N}_{2}}}=\frac{{{e}^{-10\lambda t}}}{{{e}^{-\lambda t}}}=\frac{1}{{{e}^{9\lambda t}}}\] Given that \[\frac{{{N}_{1}}}{{{N}_{2}}}=\frac{1}{e},\]\[\therefore \]\[\frac{1}{{{e}^{9\lambda t}}}=\frac{1}{e}\]or \[9\lambda t=1\] or \[t=\frac{1}{9\lambda }\] Hence, the correction option is [d].


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