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

  • question_answer
    A radioactive isotope has a half-life of 200 years. How long will it take the activity to reduce to 1% of its original value?

    A)  330 years

    B)  460 years

    C)  660 years

    D)  920 years

    Correct Answer: C

    Solution :

    [c] \[N={{N}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\] so, for 1% decay \[\frac{1}{100}{{N}_{0}}={{N}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\Rightarrow \frac{1}{100}={{\left( \frac{1}{2} \right)}^{n}}\] \[\Rightarrow \,\,\,\,\,\,\,\,n=\frac{2}{\log 2}\Rightarrow \frac{t}{T}=\frac{2}{\log 2}\Rightarrow t=6.6T\] \[=6.6\times 100=660\]  years If \[\alpha \] and B are emitted simultaneously.


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