JEE Main & Advanced Physics Nuclear Physics And Radioactivity Question Bank Self Evaluation Test - Nuclei

  • question_answer
    ` Half lives of two isotopes X and Y of a material are known to be \[2\times {{10}^{9}}years\] and   \[4\times {{10}^{9}}years\,\]respectively If a planet was formed with equal number of these isotopes, then the current age  of planet, given that currently the material has 20% of X and 80% of Y by number, will be

    A)  \[2\times {{10}^{9}}years\]

    B)        \[4\times {{10}^{9}}years\,\]

    C)  \[6\times {{10}^{9}}years\]   

    D)     \[8\times {{10}^{9}}years\]

    Correct Answer: D

    Solution :

    [d] \[{{N}_{x}}=\frac{{{N}_{0}}}{2}{{e}^{-{{\lambda }_{1}}t}}=0.2{{N}_{0}}\,\,\,{{N}_{y}}=\frac{{{N}_{0}}}{2}{{e}^{-{{\lambda }_{2}}t}}=0.8{{N}_{0}}\] \[{{e}^{({{\lambda }_{1}}-{{\lambda }_{2}})}}=4\Rightarrow t=8\times {{10}^{9}}\]  years


You need to login to perform this action.
You will be redirected in 3 sec spinner