2. Solved Papers
  3. NEET
  4. Physics
  5. Nuclear Physics And Radioactivity

NEET Physics Nuclear Physics And Radioactivity NEET PYQ-Nuclear Physics

  • question_answer
    Radioactive material \['A'\] has decay constant \['8\lambda '\] and material \['B'\] has decay constant \['\lambda '\]. Initially they have same number of nuclei. After what time, the ratio of number of nuclei of material \['B'\] to that \['A'\] will be \[\frac{1}{e}\]?                                                                                                [NEET-2017]

    A)  \[\frac{1}{9\lambda }\]             

    B)       \[\frac{1}{\lambda }\]

    C)  \[\frac{1}{7\lambda }\] 

    D)       \[\frac{1}{8\lambda }\]

    Correct Answer: C

    Solution :

    [c] No option is correct
    If we take \[\frac{{{N}_{A}}}{{{N}_{B}}}=\frac{1}{e}\]
    Then     \[\frac{{{N}_{A}}}{{{N}_{B}}}=\frac{{{e}^{-8\lambda t}}}{{{e}^{-\lambda t}}}\]
    \[\frac{1}{e}={{e}^{-7\lambda t}}\]
    \[-1=-7\lambda t\]
    \[t=\frac{1}{7\lambda }\]


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