BCECE Engineering BCECE Engineering Solved Paper-2004

  • question_answer
    A radioactive substance after 48 days remains 25% of initial then find disintegration constant:

    A) \[2.89\times {{10}^{-2}}{{T}^{-1}}\]

    B)        \[3.89\times {{10}^{-3}}{{T}^{-1}}\]

    C) \[4.89\times {{10}^{-2}}{{T}^{-1}}\]

    D)        None of these

    Correct Answer: A

    Solution :

    Key Idea: \[k=\frac{2.303}{t}\log \frac{{{N}_{0}}}{{{N}_{t}}}\] where t = time = 48 days \[{{N}_{0}}=\] Initial amount of radioactive substance \[=100\] \[{{N}_{t}}=\]Initial amount of radioactive substance left after time \[t=25\]                 \[\therefore \]  \[k=\frac{2.303}{48}\log \frac{100}{25}\]                                 \[=0.0479\log 4=0.0479\times 0.6020\]                                 \[=2.89\times {{10}^{-2}}{{T}^{-1}}\]


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