KVPY Sample Paper KVPY Stream-SX Model Paper-17

  • question_answer
    At a given instant, say \[t=0,\] two radioactive substances A and B have equal activates. The ratio \[\frac{{{R}_{B}}}{{{R}_{A}}}\] of their activates after time t itself decays with time t as \[{{e}^{-\,\,3t}},\] If the half-life of A is ln2, the half- life of B is:

    A) 4In2

    B) \[\frac{\text{In}2}{2}\]

    C) \[\frac{\text{In}2}{4}\]

    D) 2In2

    Correct Answer: C

    Solution :

    \[R={{R}_{o}}^{e\,-\,\lambda t}\]
    \[\therefore \]      \[\frac{{{R}_{B}}}{{{R}_{A}}}=\frac{{{R}_{o}}e{{\,}^{-\,{{\lambda }_{{{B}^{t}}}}}}}{{{R}_{o}}{{e}^{-\,{{\lambda }_{{{B}^{t}}}}}}}\]
    \[={{e}^{-({{\lambda }_{B}}-{{\lambda }_{A}})t}}={{e}^{-3t}}\]
    \[\Rightarrow \]   \[{{\lambda }_{B}}-{{\lambda }_{A}}=3\] \[\Rightarrow \]           \[\frac{I{{n}^{2}}}{{{T}_{B}}}-\frac{In2}{In2}=3\]\[\Rightarrow \]           \[{{T}_{B}}=\frac{In2}{4}\]


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