CET Karnataka Medical CET - Karnataka Medical Solved Paper-2012

  • question_answer
    Decay constants of two radio-active samples A and B are 15x and 3x respectively. They have equal number of initial nuclei. The ratio of the number of nuclei left in A and B after a time \[\frac{1}{6x}\]is

    A)  \[e\]      

    B)  \[{{e}^{2}}\]     

    C)  \[{{e}^{-1}}\]   

    D)  \[{{e}^{-2}}\]

    Correct Answer: D

    Solution :

    : According to radioactive decay, \[N={{N}_{0}}{{e}^{-\lambda t}}\] where \[{{N}_{0}}\]= Initial number of nuclei at t = 0 N= Number of nuclei left undecayed after time \[\lambda \]= Decay constant For A, \[{{N}_{A}}={{N}_{0A}}{{e}^{^{^{-(15x)(1/6x)}}}}\] \[={{N}_{0A}}{{e}^{-5/2}}\] For B,  \[{{N}_{0B}}{{e}^{-(3x)(1/6x)}}\] \[{{N}_{0B}}{{e}^{-1/2}}\] As per question, \[{{N}_{0}}_{A}={{N}_{0B}}\] \[\therefore \] \[\frac{{{N}_{A}}}{{{N}_{B}}}=\frac{{{e}^{-5/2}}}{{{e}^{-1/2}}}={{e}^{-2}}\]


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