An isotope has an initial activity of 120 Bq 6 ... - JAMB Physics 2022 Question
An isotope has an initial activity of 120 Bq. 6 days later its activity is 15 Bq. What is half-life?
A
3 days
B
2 days
C
1 day
D
4 days
correct option: b
the amount left undecayed = A
the initial amount = A0
the number of half-lives that passed in a period of time = t:
\(\frac{1}{2^n} * A_0 = A\)
\(\frac{1}{2^n} * 120 = 15\)
\(\frac{1}{2^n}\) = \(\frac{15}{120}\)
\(\frac{1}{2^n}\) = \(\frac{1}{8}\)
\(\frac{1}{2^n}\) = \(\frac{1}{2^3}\)
\(2^n = 2^3\)
n = 3
6days/3 = 2 days
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