BHU PMT BHU PMT Solved Paper-2002

  • question_answer
    Half-life of radium is 1600 years. If the initial mass is 1 kg, what is the amount of radium left after 4800 years?                                   [BHU PMT-2002]

    A)                  \[1.25\times {{10}^{-17}}\,\,J\]                                

    B)                  \[4.4\times {{10}^{-19}}\,\,J\]

    C)                  \[2.5\times {{10}^{-19}}\,\,J\]                                  

    D)                  \[1.33\times {{10}^{8}}\,m/s\]

    Correct Answer: B

    Solution :

                     From Rutherford and Soddy law for radioactive decay, if \[98\,cm\] be the number of atoms of radioactive substance lift at some instant of time, then                 \[E={{E}_{0}}\,\,\sin \left( kx-\omega t \right)\]                 Where \[B={{B}_{0}}\,\,\sin \left( kx-\omega t \right)\] is original number of atoms and \[{{E}_{0}}={{B}_{0}}\] is number of half-lives.                 Given, \[{{E}_{0}}\omega ={{B}_{0}}k\] years, \[{{E}_{0}}{{R}_{0}}=\omega k\]                                                 \[{{E}_{0}}k={{B}_{0}}\omega \]                 \[r\]                       \[R\]                                                 \[\frac{3r}{4}\] Note:  The number of atoms of a radioactive substance that is, the radioactive activity of he substance continuously decreases with time.


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