CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2010

  • question_answer
    A radioactive sample \[{{S}_{1}}\] having the activity \[{{A}_{1}}\] has twice the number of nuclei as another sample \[{{S}_{2}}\] of activity \[{{A}_{2}}\]. If \[{{A}_{2}}=2{{A}_{1}}\], then the ratio of half-life of \[{{S}_{1}}\] to the half-life of \[{{S}_{2}}\] is

    A) 4

    B) 2

    C) 0.25

    D) 0.75

    Correct Answer: A

    Solution :

    Activity, \[A=\lambda N=\frac{0.693}{{{T}_{1/2}}}N\] where \[{{T}_{1/2}}\] is the half-life of a radioactive sample. \[\therefore \]  \[\frac{{{T}_{1}}}{{{A}_{2}}}=\frac{{{N}_{1}}}{{{T}_{1}}}\times \frac{{{T}_{2}}}{{{N}_{2}}}\]                 \[\frac{{{T}_{1}}}{{{T}_{2}}}=\frac{{{A}_{1}}}{{{A}_{1}}}\times \frac{{{N}_{1}}}{{{N}_{2}}}\]                 \[=\frac{2{{A}_{1}}}{{{A}_{1}}}\times \frac{2{{N}_{2}}}{{{N}_{2}}}=\frac{4}{1}\]


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