AMU Medical AMU Solved Paper-2001

  • question_answer
    The activity of a radioactive element falls to \[\left( \frac{1}{32} \right)\] of its original value in 50 days. The \[{{t}_{1/2}}\] of the substance is

    A)  20 days                               

    B)  15 days

    C)  10 days                               

    D)  5 days

    Correct Answer: C

    Solution :

                     Key Idea             \[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{n}}\] where n = number of half-life period \[{{N}_{0}}=\] initial concentration N = concentration left after n half-life period.                 \[T=n{{\times }_{1/2}}\] where, T = total time                 (-1/2 = half-life period Here,     \[N=\frac{1}{32},\,\,\,T=50\] days                 \[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{n}}\]                 \[\frac{1}{32}={{\left( \frac{1}{2} \right)}^{n}}\]                 \[{{\left( \frac{1}{2} \right)}^{5}}={{\left( \frac{1}{2} \right)}^{n}}\]                 \[n=5\] \[\because \]     \[T=n\times {{t}_{1/2}}\] \[\therefore \]  \[{{t}_{1/2}}=\frac{T}{n}=\frac{50}{5}=10\] day


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