Neco 2024 Physics Question 11

Practice objective / multiple choice question 11 from the 2024 Neco Physics examination.

Neco 2024 Physics Objective / Multiple Choice Hard Difficulty
Question 11 NECO • 2024 • PHYSICS • objective

A mixture contains two radioactive isotopes, A and B. Isotope A has a half‑life of \(10\ \text{min}\) and isotope B has a half‑life of \(30\ \text{min}\). At time \(t = 0\) the total activity of the mixture is \(5.0 \times 10^{5}\ \text{Bq}\). After \(20\ \text{min}\) the total activity has decreased to \(2.0 \times 10^{5}\ \text{Bq}\). Assuming both isotopes decay independently and that the activity of each isotope is given by \(A = \lambda N\) where \(\lambda = \frac{\ln 2}{T_{1/2}}\), determine the initial number of atoms of isotope A and of isotope B in the sample.

Answer Options

A. Initial atoms of A \\(\\approx 3.90\\times10^{6}\\) atoms; initial atoms of B \\(\\approx 9.20\\times10^{6}\\) atoms.
B. Initial atoms of A \\(\\approx 5.12\\times10^{6}\\) atoms; initial atoms of B \\(\\approx 7.84\\times10^{6}\\) atoms.
C. Initial atoms of A \\(\\approx 4.36\\times10^{5}\\) atoms; initial atoms of B \\(\\approx 8.57\\times10^{7}\\) atoms.
Correct Answer D. Initial atoms of A \(\approx 4.36\times10^{6}\) atoms; initial atoms of B \(\approx 8.57\times10^{6}\) atoms.
Correct Answer
D
Correct Option:
Initial atoms of A \(\approx 4.36\times10^{6}\) atoms; initial atoms of B \(\approx 8.57\times10^{6}\) atoms.

About This Question

This is Neco 2024 Physics Question 11. It is one of the objective questions from the 2024 Neco Physics examination.

Difficulty level: Hard .

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