The shape of the lesson
By the end of the lesson, learners can
- Split it, or join it: Trigger a fission split and a fusion join, and watch the energy released by each.
- Opposite paths, same release: One breaks heavy nuclei apart, the other forces light nuclei together, and both give out energy.
- Fission: heavy nucleus splits into two lighter ones, plus neutrons and energy.
- Fusion: light nuclei join into a heavier one, releasing energy.
- Both: release energy from the nucleus.
One picture every idea returns to
Nuclear fission splits a large nucleus into smaller ones, releasing energy and neutrons that can trigger a chain reaction, the process in nuclear reactors. Nuclear fusion joins light nuclei into a heavier one, releasing energy, the process that powers the Sun and stars.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Splitting, and joining.. Two opposite tricks unlock the energy of the nucleus. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Split it, or join it | Trigger a fission split and a fusion join, and watch the energy released by each. Project tab 5 of the lab (Fission and fusion) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Opposite paths, same release | One breaks heavy nuclei apart, the other forces light nuclei together, and both give out energy. | Anticipation / Reaction Guide |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 14 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Opposite paths, same release, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Anticipation / Reaction Guide
Before the lesson, students mark five statements true or false. After the teaching they mark them again and justify any change of mind in one sentence each. The statements come from the examiner traps below.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Fission splits a heavy nucleus while fusion joins light nuclei, the opposite processes, yet both release energy. | Fusion needs extreme temperatures and pressures, which is why it happens in stars but is hard to achieve on Earth. |
Nuclear fission and fusion: worksheet
6 questions, 14 marks. Written in the style of the papers; no past paper question is reproduced.
Describe what happens to a heavy nucleus in nuclear fission.
Explain how a chain reaction is set up in a sample of fissionable material.
Describe what happens in nuclear fusion.
Explain why fusion can only happen at very high temperatures.
State which process, fission or fusion, is used in a nuclear power station, and which provides the energy of the Sun.
State the main difference between fission and fusion, and one thing that is the same about them.
Answer key and marking notes
- It absorbs a neutron and becomes unstable. ✓
- It splits into two lighter nuclei, releasing energy. ✓
- Two or three more neutrons are also released. ✓
- Each fission releases two or three neutrons. ✓
- These neutrons are absorbed by other nuclei, making them split too. ✓
- If enough nuclei are present, the reaction keeps itself going. ✓
- Two light nuclei join together to form a heavier nucleus. ✓
- Energy is released. ✓
- The two nuclei are positively charged and repel each other. ✓
- Only at very high temperatures do they move fast enough to get close enough to join. ✓
- A nuclear power station uses fission. ✓
- The Sun is powered by fusion. ✓
- Difference: fission splits a heavy nucleus into lighter ones, while fusion joins light nuclei into a heavier one. ✓
- Same: both release energy from the nucleus. ✓
5 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
What is nuclear fission?
- AA large nucleus splits into smaller nuclei, releasing energy.
- BTwo small nuclei join to form a larger nucleus.
- CA nucleus emits an alpha particle.
- DElectrons are removed from an atom.
What is nuclear fusion?
- ATwo light nuclei join to form a heavier nucleus, releasing energy.
- BA large nucleus splits into two smaller nuclei.
- CA nucleus captures an electron.
- DA nucleus emits a gamma ray only.
Why does nuclear fusion only happen at extremely high temperatures and pressures?
- AThe nuclei are positively charged and repel, so they need very high energy to get close enough to join.
- BNuclei only move at low temperatures.
- CHigh pressure adds electrons to the nuclei.
- DHeat gives the nuclei a negative charge.
In a fission chain reaction, what keeps the reaction going?
- AThe neutrons released by each fission go on to cause further fissions.
- BElectrons released keep splitting more nuclei.
- CGamma rays trigger the next fission.
- DThe fragments rejoin and split again.
Where does nuclear fusion happen naturally on a huge scale?
- Ain the Sun and other stars
- Bin nuclear power stations on Earth
- Cinside smoke alarms
- Din a household battery
Quiz key
In fission a large, unstable nucleus (such as uranium) splits into smaller nuclei, releasing energy and usually two or three neutrons. Joining small nuclei is fusion, not fission.
In fusion two light nuclei (such as hydrogen isotopes) join to form a heavier nucleus, releasing a large amount of energy. Splitting a heavy nucleus is fission, the opposite process.
Both nuclei are positively charged and repel strongly, so they must be moving extremely fast (very high temperature) and be pushed very close (very high pressure) to fuse. These conditions exist in the core of stars.
Each fission releases neutrons, and these go on to split further nuclei, releasing yet more neutrons: a chain reaction. It is the neutrons, not electrons or gamma rays, that sustain it.
Fusion powers the Sun and other stars, where hydrogen nuclei fuse into helium under immense temperature and pressure. Power stations on Earth currently use fission, not fusion.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.