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QNEET-2016-Ph-1172: NEET 2016 Physics - Class 12 NEET-2016-Ph-1172 Solution: The half-life of a radioactive substance is 30 minutes. The…
The half-life of a radioactive substance is 30 minutes. The time (in minutes) taken between 40% decay and 85% decay of the same radioactive substance is 15 30 45 60
Multiple Choice Options
- A 15
- B 30
- C 45
- D 60
Step-by-Step Verified Solution
N 0
= Nuclei at time t = 0
N 1
= Remaining nuclei after 40% decay
= (1 � 0.4) N 0
= 0.6 N 0
N 2
= Remaining nuclei after 85% decay
= (1 � 0.85) N 0
= 0.15 N 0
_ N 2 N 1 = 0.15 N 0 0.6 N 0 = ( 1 2 ) 2
Hence number of half-lives is 2, so the time needed
is :
t = 2 _ 30 = 60 mints