NEET Sample Paper NEET Sample Test Paper-57

  • question_answer
    C Number of nuclei of a radioactive substance at time t = 0 are 2000 and 1800 at time t = 2sec. Number of nuclei left after t = 6sec is:

    A) 1442                            

    B) 1554    

    C) 1652                            

    D) 1458

    Correct Answer: D

    Solution :

    [d] \[N={{N}_{{}^\circ }}{{e}^{-\lambda t}}\] \[1800=2000{{e}^{-\lambda \times 2}}\] \[\frac{9}{10}={{e}^{-2\lambda }}\Rightarrow {{e}^{-\lambda }}={{\left[ \frac{9}{10} \right]}^{1/2}}\] No. of nuclei left after 6s \[N={{N}_{{}^\circ }}{{e}^{-\lambda T}}\] \[N=2000{{\left[ \frac{9}{10} \right]}^{1/2\times 6}}=2000\times {{\left[ \frac{9}{10} \right]}^{3}}\] \[N=2000\times \frac{729}{1000}=1458\]


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