JEE Main & Advanced Sample Paper JEE Main - Mock Test - 31

  • question_answer
    A fraction fi of radioactive sample remains in one mean life and a fraction \[{{f}_{2}}\] remains in one half life, then-

    A) \[{{f}_{1}}={{f}_{2}}\]          

    B)        \[{{f}_{1}}=\frac{{{f}_{2}}}{2}\]

    C) \[{{f}_{1}}<{{f}_{2}}\]       

    D)        \[{{f}_{1}}>{{f}_{2}}\]

    Correct Answer: C

    Solution :

    [c] \[N={{N}_{0}}\,{{e}^{-\lambda t}}\,\] \[t={{t}_{mean}}=\frac{1}{\lambda }\] \[\therefore \,{{f}_{1}}=\frac{N}{{{N}_{0}}}{{e}^{-1}}=\frac{1}{e}.\] \[t={{t}_{(half)}}=\frac{\ell n2}{\lambda }\]       \[\therefore \,{{f}_{2}}=\frac{N}{{{N}_{0}}}{{e}^{-In2}}=\frac{1}{2}\] \[\therefore {{f}_{2}}>{{f}_{1}}\].       


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