AMU Medical AMU Solved Paper-2002

  • question_answer
    A sample of radioactive substance with a \[{{t}_{1/2}}=3\] days was found to contain 3g of it, when received exactly after 12 days. The amount of radioactive substance when it was sealed

    A)  48 g                                      

    B)  12 g

    C)  24 g                                      

    D)  6g

    Correct Answer: A

    Solution :

                     Key Idea \[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{n}}\] where,               n = number of half-life period \[{{N}_{0}}\] = initial corcentration N = concentration left after n half-life period and             \[T=n\propto {{t}_{1/2}}\]           where, \[{{t}_{1/2}}=\] half-life period                 T = total time Here,     \[{{t}_{1/2}}=3\] days, T = 12 days \[\therefore \]  \[n=\frac{12}{3}=4\]                 \[N=3\,g\] \[\therefore \]              \[\frac{3}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{4}}\]                 \[\frac{3}{{{N}_{0}}}=\frac{1}{16}\]                 \[{{N}_{0}}=48\,\,g\]


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