BVP Medical BVP Medical Solved Paper-2015

  • question_answer
    An unstable element is produced in a nuclear reaction of a constant rate \[\frac{Mgx}{3}\]. Its disintegration constant is \[\eta \]. Find the number of nuclei after time t, if initially it was zero.

    A)  \[2mg\,[1+{{(\eta /L)}^{2}}]\]

    B)  \[mg\,[1+{{(\eta /L)}^{2}}]\]

    C)  \[\frac{mg}{2}\,[1+{{(\eta /L)}^{2}}]\]

    D)  \[4mg\,[1+{{(\eta /L)}^{2}}]\]

    Correct Answer: D

    Solution :

                    For radioactive decay, we can write \[\frac{dN}{dt}\eta -\lambda N\]                 or            \[\int\limits_{0}^{N}{\frac{dN}{\eta -\lambda N}}=\int\limits_{0}^{t}{dt}\]                 or,          In \[\left( \frac{\eta -\lambda N}{\eta } \right)=-\lambda t\]                 or            \[\frac{\eta -\lambda N}{\eta }={{e}^{-\lambda t}}\]                 or,          \[N=\frac{\eta }{\lambda }[1-{{e}^{-\lambda t}}]\]


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