Pearson Edexcel International GCSE in Physics · 4PH1 · Free · no account needed
Half-Life — exam questions
11 original Incandio exam-style questions on half-Life, 25 marks, about 25 minutes of writing. Each one carries the command word, the tariff and the specification statement it assesses, exactly as a paper presents them. This is an original Incandio practice question, written to reflect the structure and demands of the qualification. It is not an official Pearson Edexcel past-paper question.
This is the practice set for Half-Life — the lesson that teaches it. Read the lesson first if the idea is new; come here when you want to find out whether you can turn it into marks. Completely free, no account needed to read.
What these questions ask of you
8 command words run through this set, and on Pearson Edexcel International GCSE Physics each one means something precise. Answering the wrong command is the commonest way a candidate who understands the lesson still loses the mark.
- State what is meant by (1–2 marks)
- the definition
- Which (1 mark)
- one option chosen from the set given
- Calculate (1–5 marks)
- select the equation, substitute, evaluate — and state the unit Misread as: giving a bare number with no equation and no unit
- Explain (2–4 marks)
- the physics that causes it, set out as a line of reasoning Misread as: describing the change without giving the physical reason for it
- Suggest (1–3 marks)
- a plausible answer applying taught physics to an unfamiliar arrangement
- Give (1–2 marks)
- a short factual answer
- Determine (1–4 marks)
- a value obtained by combining a reading or gradient with a relationship
- Describe (2–4 marks)
- developed, linked statements of what happens — including a named direction where one exists
Assessed on Paper 1 (4PH1/1P) and Paper 2 (4PH1/2P), against AO1, AO2, AO3.
Where these sit in the specification
Pearson Edexcel International GCSE Physics (4PH1) — statements 7.11 · 7.12 · 7.13. Incandio is aligned to this specification; it is not published by, endorsed by or affiliated with Pearson, and it reproduces none of Pearson's wording.
The 11 questions
Answer them on paper, then open the lesson's exam practice to have them marked. The mark scheme, the accepted and rejected answers and the annotated model answer are in Incandio and are not printed here — an answer beside its question is not practice.
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A sample of a radioactive isotope was placed near a detector. The background count rate had already been measured as 20 counts per minute, and the readings below have had it subtracted.
Figure 1 — corrected count rate against time for the sample. Plotted as a line; the graph is drawn in Incandio and the readings are below. Time / hours Corrected count rate / counts per minute 0 640 3 452 6 320 9 226 12 160 18 80 24 40 30 20 (a)
(1)Give
Give one reason why the background count rate was subtracted from the readings.
A sample of a radioactive isotope was placed near a detector. The background count rate had already been measured as 20 counts per minute, and the readings below have had it subtracted.
Figure 1 — corrected count rate against time for the sample. Plotted as a line; the graph is drawn in Incandio and the readings are below. Time / hours Corrected count rate / counts per minute 0 640 3 452 6 320 9 226 12 160 18 80 24 40 30 20 (b)
(2)Determine
Determine the half-life of this isotope, using Figure 1.
A sample of a radioactive isotope was placed near a detector. The background count rate had already been measured as 20 counts per minute, and the readings below have had it subtracted.
Figure 1 — corrected count rate against time for the sample. Plotted as a line; the graph is drawn in Incandio and the readings are below. Time / hours Corrected count rate / counts per minute 0 640 3 452 6 320 9 226 12 160 18 80 24 40 30 20 ............................ hours
(c)
(3)Calculate
Calculate the corrected count rate that would be expected 42 hours after the start.
A sample of a radioactive isotope was placed near a detector. The background count rate had already been measured as 20 counts per minute, and the readings below have had it subtracted.
Figure 1 — corrected count rate against time for the sample. Plotted as a line; the graph is drawn in Incandio and the readings are below. Time / hours Corrected count rate / counts per minute 0 640 3 452 6 320 9 226 12 160 18 80 24 40 30 20 ............................ counts per minute
(d)
(2)Explain
Explain why the readings taken late in the experiment are less reliable than those taken at the start.
A sample of a radioactive isotope was placed near a detector. The background count rate had already been measured as 20 counts per minute, and the readings below have had it subtracted.
Figure 1 — corrected count rate against time for the sample. Plotted as a line; the graph is drawn in Incandio and the readings are below. Time / hours Corrected count rate / counts per minute 0 640 3 452 6 320 9 226 12 160 18 80 24 40 30 20 (Total for Question 1 = 8 marks)
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(1)State what is meant by
State what is meant by the half-life of a radioactive isotope.
(Total for Question 2 = 1 mark)
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(1)Which
Which statement about radioactive decay is correct?
Statement A Every nucleus decays after exactly one half-life. B Decay of an individual nucleus is random and cannot be predicted. C Heating a sample makes it decay faster. D Activity falls to zero after two half-lives. (Total for Question 3 = 1 mark)
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(3)Calculate
A sample has an activity of 4800 Bq. The half-life of the isotope is 8 days. Calculate the activity after 32 days.
activity after 32 days = ............................ Bq
(Total for Question 4 = 3 marks)
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(3)Explain
Explain why the count rate measured by a detector never falls to zero, however long a radioactive sample is left.
(Total for Question 5 = 3 marks)
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(2)Suggest
An isotope used to trace a leak in an underground water pipe has a half-life of six hours. Suggest why an isotope with a half-life of six years would be unsuitable.
(Total for Question 6 = 2 marks)
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(3)Describe
Describe what is meant by saying that radioactive decay is a random process, and how a half-life can still be predicted.
(Total for Question 7 = 3 marks)
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(4)Determine
A sample of a radioactive isotope has an activity of 640 Bq. After 18 hours the activity has fallen to 40 Bq. Determine the half-life of the isotope.
half-life = ............................ hours
(Total for Question 8 = 4 marks)
Have them marked, then defend the answer
Practice tells you the mark; teaching it back tells you whether you understand it. On Incandio a topic counts as mastered only once you have taught it and defended it.
- Mark these questions — 11 questions, marked on Incandio against the authored scheme, with the mistake you actually made named.
- Teach it — explain half-Life to Ember, an AI pupil who does not have it yet and asks the awkward question.
- Defend it — argue it against Marie Curie over three rounds, marked against descriptors you can read first.
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Back to the lesson
- Half-Life — Half of what is left, every time — which is why a radioactive sample never quite runs out.
- All of Incandio Physics · Incandio Exam Practice