RAJASTHAN PMT Rajasthan - PMT Solved Paper-2009

  • question_answer
    If a radioactive substance decays \[\frac{\text{1}}{\text{16}}\text{th}\] of its original amount in 2 h, then the half-life of that substance is

    A)  15 min                                 

    B)  30 min

    C)  45 min                 

    D)         None of these

    Correct Answer: B

    Solution :

    For a radioactive substance                 \[N={{N}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\]                 \[\frac{{{N}_{0}}}{16}={{N}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\] \[\therefore \]  \[n=4\] \[\because \]     \[t=n\times T\] \[\therefore \]  \[T=\frac{t}{n}=\frac{2}{4}h\]                 \[=\frac{2\times 60}{4}\min =30\min \]


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