NEET Physics Nuclei Questions Solved

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Half-life of a radioactive substance is 20 minutes. Difference between points of time when it is 33% disintegrated and 67% disintegrated is approximately 
(a) 10 min           (b) 20 min
(c) 30 min           (d) 40 min

(b) λ=0.693T1/2=0.69320=0.03465

Now time of decay t=2.303λlogN0N

t1=2.3030.03465log10067=11.6 min

and t2=2.3030.03465log10033=32 min

Thus time difference between points of time

=t1-t2=32-11.6=20.4 min20 min

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