Punjab Medical Punjab - MET Solved Paper-2003

  • question_answer
    The half-life of a radioactive substance is 3.6 days. How much of \[20\,\,mg\] of this radioactive substance will remain after 36 days:

    A) \[0.0019\,\,mg\]                              

    B) \[1.019\,\,mg\]

    C) \[1.109\,\,mg\]                

    D) \[0.019\,\,mg\]

    Correct Answer: D

    Solution :

    Half-life\[{{T}_{1/2}}=3.6\,\,days\] Initial quantity\[{{N}_{0}}=20\,\,mg\] Total line\[=36\,\,days\] The number of half lives                 \[n=\frac{t}{{{T}_{1/2}}}=\frac{36}{3.6}=10\] Hence, mass of radioactive substance left after 10 half lives                 \[N={{N}_{0}}\times {{\left( \frac{1}{2} \right)}^{n}}\]                 \[=20\times \frac{1}{1024}=0.019\,\,mg\]


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