RAJASTHAN PMT Rajasthan - PMT Solved Paper-2003

  • question_answer
    The half life of a certain radioactive substance is 12 days. The time taken for  \[\frac{7}{8}\] of sample to decay is

    A)  36 days               

    B)         12 days

    C)  4 days                 

    D)         24 days

    Correct Answer: A

    Solution :

    Given half life, T= 12 days Fraction decayed\[=\frac{7}{8}\]                                             \[\therefore \]Fraction undecayed\[=1-\frac{7}{8}=\frac{1}{8}\] \[\therefore \]                               \[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{n}}\] \[\Rightarrow \]                                               \[\frac{1}{8}={{\left( \frac{1}{2} \right)}^{n}}\] or                                            \[{{\left( \frac{1}{2} \right)}^{3}}={{\left( \frac{1}{2} \right)}^{n}}\] \[\therefore \] Time, taken for \[\frac{7}{8}th\]sample to decayed\[t=3T=3\times 12=36\] days


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