BHU PMT BHU PMT (Screening) Solved Paper-2006

  • question_answer
    What is the disintegration constant of radon, if the number of its atoms diminishes by 18% in 24 h?

    A)  \[2.1\times {{10}^{-3}}{{s}^{-1}}\]                          

    B) \[2.1\times {{10}^{-4}}{{s}^{-1}}\]

    C)  \[2.1\times {{10}^{-5}}{{s}^{-1}}\]          

    D) \[2.1\times {{10}^{-6}}{{s}^{-1}}\]

    Correct Answer: D

    Solution :

                     The percentage of radioactive substance left behind after time t, \[\frac{N}{{{N}_{0}}}=(100-18)%=82%\] Also       \[\frac{N}{{{N}_{0}}}={{e}^{-\lambda t}}\] \[\therefore \]  \[\frac{82}{100}={{e}^{-(\lambda \times 24\times 60\times 60)}}\] Or           \[24\times 60\times 60\times \lambda =\log \left( \frac{100}{82} \right)\] \[\therefore \]  \[\lambda =2.1\times {{10}^{-6}}{{s}^{-1}}\]


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