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Calculate the number of half lives elapsed, the end of which, the activity of a radioactive sample decrease by 90%. |
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Answer» SOLUTION :The change in activity with time follows the same was that of number of radioactive atoms. `THEREFORE`PERCENTAGE of radioactive atoms LEFT undecayed. 100-90%=10% i.e., `N/N_0=1/10` From `(N/N_0)=(1/2)^n` [where n=no. of half lives elapsed ] `(1/2)^n =1/10` or, `2^n=10` or , n log 2 = log 10 or , `n=1/0.3010`=3.3 Thus, at the end of 3.3 half lives, the activity and hence the number of atoms) would have DECREASED by 90%. |
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