NEET Physics Nuclei Questions Solved

NEET - 2008

Two radioactive material X1 and X2 have decay constants 5λ and λ respectively. If initially they have the same number of nuclei of X1to that of X2 will be 1eafter a time 

(a)λ                                     (b)12λ

(c)14λ                                 (d)eλ

If N is the number of radioactive nuclei present at some instant, then

        N=N0e-λt

The constant N0 represents the number of radioactive nuclei at t=0

Now,            N1N2=e-λ1te-λ2t

or              N1N2=e-5λte-λt=e-4λt

but          N1N2=1e                      as provided

Therefore,    1e=1e4λt

or           4λt=1

or           t=14λ

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