JEE Mains · Physics · STD 12 - 13. Nuclei
The half life of a radioactive substance is \(5\) years. After \(x\) years a given sample of the radioactive substance gest reduced to \(6.25 \%\) of its initial value of \(x\) is ...............
- A \(20\)
- B \(19\)
- C \(21\)
- D \(22\)
Answer & Solution
Correct Answer
(A) \(20\)
Step-by-step Solution
Detailed explanation
\(T 1 / 2=5\) year \(N = N _{0}\left(\frac{1}{2}\right)^{\text {No of half lives }}\) \(\frac{ N }{ N _{0}}=\frac{1}{16}=\left(\frac{1}{2}\right)^{4}\) Time \(=4\) half lives \(=20\) years
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