IB Physics HL E.3.21 Activity equation Question Bank

Practise IB Physics HL E.3.21 by applying activity equation concepts to exam-style physics questions.

Exam points

identify the relevant physical quantity, model or diagram
apply the correct equation and units to the evidence
justify the result using conservation laws, fields or energy relationships

[Maximum number: 2]

A short-range attractive force operates between nucleons.

A sample of potassium has a mass of 5.00 g . The sample contains 0.012 % of potassium-40 by mass. The remainder of the sample is a stable nuclide of potassium. The half-life of potassium-40 is $1.28 \times 10^{9}$ years.

The mass of one mole of potassium is $39.1 \mathrm{~g} \mathrm{~mol}^{-1}$ .

Determine the initial activity of the sample.

$\begin{aligned} N_{0}=\frac{5}{39.1} \times 0.00012 \times 6.02 \times 10^{23}=9.24 \times 10^{18} A_{o}=\lambda N_{o}=\left(1.72 \times 10^{-17}\right)\left(9.24 \times 10^{18}\right)=159 \mathrm{~Bq} \end{aligned}$

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E.3.21 (HL)—Activity equation question 1