JEE Main & Advanced JEE Main Solved Paper-2016

  • question_answer
    Half-lives of two radioactive elements A and B are 20 minutes and 40 minutes, respectively. Initially, the samples have equal number of nuclei. After 80 minutes , the ratio of decayed numbers of A and B nuclei will be :- [JEE Main Solved Paper-2016 ]

    A) 5 : 4                                       

    B) 1 : 16

    C)  4 : 1                                      

    D) 1 : 4

    Correct Answer: A

    Solution :

                    \[t=80\min =4{{T}_{A}}=2{{T}_{B}}\] \[\therefore \]no. of nuclei of A decayed \[={{N}_{0}}-\frac{N}{{{2}^{4}}}=\frac{15{{N}_{0}}}{16}\] \[\therefore \]no. of nuclei of B decayed \[={{N}_{0}}-\frac{N}{{{2}^{2}}}=\frac{3{{N}_{0}}}{4}\]required ratio \[=\frac{5}{4}\]


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