JEE Main & Advanced JEE Main Paper (Held On 22 April 2013)

  • question_answer
    The half ? life of a radioactive element A is the same as the mean-life of another radioactive element B. Initially both substances have the same number of atoms, then :     JEE Main  Online Paper (Held On 22 April 2013)

    A)  A and B both decay at the same rate always

    B)  A and B will decay at the same rate initially

    C)  A will decay at a faster rate B initially

    D)  B will decay at faster rate A initially

    Correct Answer: D

    Solution :

     \[{{\left( {{T}_{1/2}} \right)}_{A}}={{\left( {{t}_{mean}} \right)}_{B}}\] \[\Rightarrow \]               \[\frac{0.693}{{{\lambda }_{A}}}=\frac{1}{{{\lambda }_{B}}}\Rightarrow {{\lambda }_{A}}=0.693{{\lambda }_{B}}\] or            \[{{\lambda }_{A}}<{{\lambda }_{B}}\] Also rate of decay \[=\lambda N\] Initially number of atoms (N) of both are equal but since \[{{\lambda }_{B}}>{{\lambda }_{A}},\] therefore B will decay at a faster rate than A


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