NEET Physics Nuclei Questions Solved

Two radioactive substances A and B have decay constants 5λ and λ respectively. At t=0 they have the same number of nuclei. The ratio of number of nuclei of A to those of B will be 1e2 after a time interval

(a) 14λ                                          (b) 4λ

(c) 2λ                                            (d) 12λ

(d) Number of nuclei remained after time t can be wriiten as 


where, N0 is initial number of nuclei of both the substances.

                 N1=N0e-5λt                              ...(i)

and           N2=N0e-λt                               ...(ii)

Dividing Eq. (i) by Eq. (ii), we obtain 

         N1N2=e-5λ+λt=e-4λt = 1e4λt

But, we have given          


Hence,        1e2=1e4λt

Comparing the powers, we get

        2=4λt        or     t=24λ=12λ


Difficulty Level:

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