JEE Main & Advanced Sample Paper JEE Main - Mock Test - 11

  • question_answer
    The half-life of a radioactive nucleus is 50 days. The time interval \[({{t}_{2}}-{{t}_{1}})\] between the time \[{{t}_{2}}\]when \[\frac{2}{3}\] of it has decayed and the time \[{{t}_{1}}\] when \[\frac{1}{3}\] of it had decayed is

    A) 30 days                        

    B) 50 days

    C) 60 days                        

    D) 15 days

    Correct Answer: B

    Solution :

    \[{{N}_{1}}={{N}_{0}}{{e}^{-\lambda t}}\]    \[{{N}_{1}}=\frac{1}{3}{{N}_{0}}\]
    \[\frac{{{N}_{0}}}{3}={{N}_{0}}{{e}^{-\lambda {{t}_{2}}}}\]
    \[\Rightarrow \,\,\,\frac{1}{3}={{e}^{-\lambda {{t}^{2}}}}\]                ...(i)
    \[{{N}_{2}}=\frac{2}{3}{{N}_{0}}\]
    \[\frac{2}{3}{{N}_{0}}={{N}_{0}}{{e}^{-\lambda {{t}_{1}}}}\]
    \[\Rightarrow \,\,\,\frac{2}{3}={{e}^{-\lambda {{t}_{1}}}}\]                  ...(ii)
    Dividing equation (i) by equation (ii)
    \[\frac{1}{2}={{e}^{-\lambda \,\,({{t}_{2}}-{{t}_{1}})}}\].
    \[\lambda ({{t}_{2}}-{{t}_{1}})=In\,2\]
    \[{{t}_{2}}-{{t}_{1}}=\frac{In\,2}{\lambda }={{T}_{1/2}}=50\] days


You need to login to perform this action.
You will be redirected in 3 sec spinner