CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2001

  • question_answer
    Three fourth of the active nuclei present in a radioactive sample decay in 3/4 sec. The half life of the sample is:

    A)  \[\frac{1}{2}\sec \]                        

    B) \[1\,\sec \]

    C)  \[\frac{3}{8}\sec \]                        

    D) \[\frac{3}{4}\sec \]

    Correct Answer: C

    Solution :

    If \[\frac{3}{4}\] part decays If means \[\frac{1}{4}\]part remain undecayed Now from the formula \[N={{N}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\] \[\frac{1}{4}={{\left( \frac{1}{2} \right)}^{n}}\] \[{{\left( \frac{1}{2} \right)}^{2.}}={{\left( \frac{1}{2} \right)}^{n}}\]         So,          \[n=2\] \[n\times {{T}_{1/2}}=t\] \[2\times {{T}_{1/2}}=\frac{3}{4}\]                 Thus      \[{{T}_{1/2}}=\frac{3}{8}\sec \]


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