The half life of a radioactive substance is 20 minutes. In how much time, the activity of substance drops to…

The half life of a radioactive substance is 20 minutes. In how much time, the activity of substance drops to 116th of its initial value?
  1. 80 minutes
  2. 20 minutes
  3. 40 minutes
  4. 60 minutes

Solution

Activity of substance is given by, A=A02n, where n is the number of half-lives.

Now, A016=A02n⇒n=4

Therefore,

n=tT12⇒t=4T12=4×20 min=80 min

Asked in: NEET 2023 (All India)

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