Pearson Edexcel International GCSE in Physics · 4PH1 · Free · no account needed
Chain Reactions and Reactors — exam questions
11 original Incandio exam-style questions on Chain Reactions and Reactors, 27 marks, about 27 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 Chain Reactions and Reactors — 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.
- Which (1 mark)
- one option chosen from the set given
- State (1 mark)
- one precise fact or definition
- Give (1–2 marks)
- a short factual answer
- Describe (2–4 marks)
- developed, linked statements of what happens — including a named direction where one exists
- 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
- Compare (2–4 marks)
- explicit comparison naming both cases
- Suggest (1–3 marks)
- a plausible answer applying taught physics to an unfamiliar arrangement
- Identify (1–2 marks)
- the correct item selected from what is shown
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 7.21 · 7.22 · 7.20. 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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The operators of a reactor keep a record of the average number of neutrons from each fission that go on to cause another fission. They call this number k. The record below covers one morning's operation.
Table 1 — one morning in the control room Time Control rods Value of k 06:00 fully lowered 0.85 07:00 partly raised 1.04 09:00 adjusted slightly 1.00 11:30 fully lowered 0.62 (a)
(1)Identify
Identify the time in Table 1 at which the reaction was exactly steady.
The operators of a reactor keep a record of the average number of neutrons from each fission that go on to cause another fission. They call this number k. The record below covers one morning's operation.
Table 1 — one morning in the control room Time Control rods Value of k 06:00 fully lowered 0.85 07:00 partly raised 1.04 09:00 adjusted slightly 1.00 11:30 fully lowered 0.62 (b)
(3)Explain
Explain what was happening to the reaction at 07:00, using Table 1.
The operators of a reactor keep a record of the average number of neutrons from each fission that go on to cause another fission. They call this number k. The record below covers one morning's operation.
Table 1 — one morning in the control room Time Control rods Value of k 06:00 fully lowered 0.85 07:00 partly raised 1.04 09:00 adjusted slightly 1.00 11:30 fully lowered 0.62 (c)
(3)Suggest
Suggest why the operators lowered the rods fully at 11:30, and what would still be needed afterwards.
The operators of a reactor keep a record of the average number of neutrons from each fission that go on to cause another fission. They call this number k. The record below covers one morning's operation.
Table 1 — one morning in the control room Time Control rods Value of k 06:00 fully lowered 0.85 07:00 partly raised 1.04 09:00 adjusted slightly 1.00 11:30 fully lowered 0.62 (Total for Question 1 = 7 marks)
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(1)Which
Which part of a reactor absorbs neutrons to control the rate of the reaction?
Part A the moderator B the fuel rods C the control rods D the shielding (Total for Question 2 = 1 mark)
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(1)State
State the purpose of the moderator in a nuclear reactor.
(Total for Question 3 = 1 mark)
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(2)Give
Give the material used for the shielding around a reactor and the reason it is needed.
(Total for Question 4 = 2 marks)
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(3)Describe
Describe how a chain reaction is set up in a sample of uranium-235.
Figure 1 — fission and a chain reaction (Total for Question 5 = 3 marks)
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(3)Explain
Explain how lowering the control rods further into the core reduces the rate of the reaction.
(Total for Question 6 = 3 marks)
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(3)Compare
Compare the job of the moderator with the job of the control rods.
(Total for Question 7 = 3 marks)
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(3)Suggest
Suggest why a reactor is designed so that the rods fall into the core when the power fails.
A fail-safe design — In many reactors the control rods are held up out of the core by electromagnets. If the electricity supply to those magnets is interrupted for any reason at all, the rods drop into the core under their own weight. Restoring them requires deliberate action by an operator.
(Total for Question 8 = 3 marks)
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(4)Explain
Explain the jobs of the moderator and of the control rods in a nuclear reactor, and why a reactor cannot run safely without both.
(Total for Question 9 = 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 Chain Reactions and Reactors to Ember, an AI pupil who does not have it yet and asks the awkward question.
- Defend it — argue it against J. Robert Oppenheimer over three rounds, marked against descriptors you can read first.
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Back to the lesson
- Chain Reactions and Reactors — Two or three neutrons from every split — and the two entirely different jobs a reactor does to them.
- All of Incandio Physics · Incandio Exam Practice