WB JEE Medical WB JEE Medical Solved Paper-2009

  • question_answer
    If \[{{n}_{t}},\]number of radio atoms are present at time t, the following expression will be a constant

    A)  \[\frac{{{n}_{t}}}{t}\]                                    

    B)  \[\ln \frac{{{n}_{t}}}{t}\]

    C)  \[\frac{d}{dt}(\ln \,nt)\]                              

    D)  \[t.{{n}_{t}}\]

    Correct Answer: C

    Solution :

                     We know that, Rate of disintegration \[=-\frac{dN}{dt}\propto N\] or \[\frac{-dN}{dt}=kN\](k = disintegration constant) Given, \[N={{n}_{t}}\]and \[t=t,\] \[\therefore \] \[\frac{-d{{n}_{t}}}{dt}=k{{n}_{t}}\] \[\Rightarrow \]               \[\frac{-d{{n}_{t}}}{{{n}_{t}}}=kdt\] or            \[\frac{-d\ln {{n}_{t}}}{dt}=k=\text{constant}\]


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