Suppose the amount of a certain radioactive substance in a sample decays from 1.30mg to 800.μg over a period of 7.57 seconds. Calculate the half life of the substance.Round your answer to 2 significant digits.
Question
Suppose the amount of a certain radioactive substance in a sample decays from 1.30mg to 800.μg over a period of 7.57 seconds. Calculate the half life of the substance.Round your answer to 2 significant digits.
Solution
To solve this problem, we need to use the formula for exponential decay, which is:
N = N0 * e^(-λt)
where: N is the final amount of the substance, N0 is the initial amount of the substance, λ is the decay constant, t is the time elapsed.
We are given that N = 800 μg, N0 = 1.30 mg = 1300 μg, and t = 7.57 s. We can plug these values into the formula and solve for λ:
800 = 1300 * e^(-λ * 7.57)
Divide both sides by 1300:
0.6154 = e^(-λ * 7.57)
Take the natural logarithm of both sides:
ln(0.6154) = -λ * 7.57
Solve for λ:
λ = -ln(0.6154) / 7.57 ≈ 0.071 s^-1
The half-life (T) of a substance is related to the decay constant by the formula:
T = ln(2) / λ
Plug in the value of λ we just found:
T = ln(2) / 0.071 ≈ 9.77 s
So, the half-life of the substance is approximately 9.77 seconds, rounded to two significant digits.
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