NEET Physics Nuclei Questions Solved


Half life of a radio-active substance is 20 minutes. The time between 20% and 80% decay will be 
(a) 20 minutes          (b) 40 minutes
(c) 30 minutes          (d) 25 minutes

(b) Here T1/2=20 minutes; we know NN0=12t/T1/2
For 20% decay NN0=80100=12t1/20..... (i)
For 80% decay NN0=20100=12t2/20..... (ii)
Dividing (ii) by (i)
14=12t2-t120 on solving we get t2-t1=40 min.

Difficulty Level:

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