J & K CET Medical J & K - CET Medical Solved Paper-2000

  • question_answer
    1 mg of radius has \[2.68\times {{10}^{18}}\] nuclei. Its half-life is 1620 yr. After 3240 yr, how many nuclei would have disintegrated?

    A)  \[1.82\times {{10}^{18}}\]                          

    B)  \[0.67\times {{10}^{18}}\]

    C)  \[1.34\times {{10}^{18}}\]                          

    D)  \[2.01\times {{10}^{11}}\]

    Correct Answer: D

    Solution :

                    \[Number\text{ }of\text{ }half-life=\frac{time\text{ }taken}{half-life}\] \[Number\text{ }of\text{ }half-life=\frac{3240}{1620}=2\] From Rutherford-Soddy law, fraction of original nuclei left is                 \[N={{N}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\] \[\Rightarrow \]               \[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{2}}=\frac{1}{4}\] Hence, number of nuclei that disintegrate \[=\frac{3}{4}\times 2.68\times {{10}^{18}}=2.01\times {{10}^{18}}\]


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