RAJASTHAN PMT Rajasthan - PMT Solved Paper-2007

  • question_answer
    If the half-life of any sample of radioactive substance is 4 days, then the fraction of sample will remain undecayed after 2 days, will be?

    A)  \[\sqrt{2}\]                                       

    B)  \[\frac{1}{\sqrt{2}}\]  

    C)  \[\frac{\sqrt{2}-1}{\sqrt{2}}\]      

    D)         \[\frac{1}{2}\]

    Correct Answer: B

    Solution :

    From Rutherford-Soddy law, the fraction left after \[n\] half-lives is                 \[N={{N}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\] where n is number of half-lives.                 \[n=\frac{time(t)}{half-life({{T}_{1/2}})}=\frac{2}{4}=\frac{1}{2}\] \[\therefore \]  \[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{1/2}}\]                 \[\Rightarrow \,\frac{N}{{{N}_{0}}}=\frac{1}{\sqrt{2}}\]


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