H1 Physics 8867 · Nov 2023PhysicsPaper 2Widespread errors
Paper 2 Q7 — Half-lives by estimation, and why alpha
Nuclear physics — half-life estimation without the exponential formula; properties of α radiation
What the examiners said
“Candidates struggled to name sources of background radiation… Few candidates appreciated that the use of alpha particles was due to their high ionising ability… A simple estimation of the activity being 12.5% after 3 half-lives and 6.25% after 4 half-lives… was sufficient (the exponential equation is not on this syllabus).”
Item 1 — background radiation
Which list contains only genuine sources of background radiation?
Examiner report: “Candidates struggled to name sources of background radiation.”
Item 2 — half-life by estimation
A source has a half-life of 30 years. Roughly how long until its activity falls below 7% of the initial value? (No exponential formula needed!)
Examiner report: “A simple estimation — 12.5% after 3 half-lives, 6.25% after 4 — was sufficient.”
Item 3 — why alpha?
Alpha sources are chosen for smoke detectors and some targeted therapies. The key property that makes α particles suitable is:
Examiner report: “Most gave a partial answer (short range); few appreciated the high ionising ability.”
Explore — count the halvings
Drag time forward and watch the activity halve each half-life. The stepping-stone percentages (50, 25, 12.5, 6.25…) are all the H1 syllabus needs.
Set t to whole multiples of the half-life and read the red stepping stones: 50 → 25 → 12.5 → 6.25%. Four halvings is the whole calculation.
Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H1 Physics 8867 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.
Made by lookang, using Claude Fable 5. More resources: iwant2study.org