Lesson 6: Nuclear Fission, Fusion & Energy Release
Demonstrating understanding of quantum phenomena, atomic structures, nuclear reactions, and special relativity.
🎯 Ngā Whāinga Akoranga | Learning Intentions
Mechanisms of nuclear fission (U-235 neutron capture, chain reactions, critical mass) and nuclear fusion (proton-proton chain in stars, D-T reactor plasma fusion), energy release calculations E = Δm c^2.
Balance nuclear reaction equations, calculate net mass difference Δm and energy yield for fission/fusion reactions, and evaluate stellar nucleosynthesis.
🎥 Media Anchor & Pedagogical Scaffold
Nuclear Fission vs Fusion Reactions
Video Clip: Nuclear fission — chain reactions, critical mass, and energy release from uranium-235 | Khan Academy Physics (Runtime: 10m 27s).
🧠 1. Before Viewing (Activate & Predict)
Why does nuclear fusion release far more energy per kilogram of fuel than nuclear fission, yet proved so difficult to harness on Earth?
👁️ 2. During Viewing (Watch With a Job)
- Fission mechanism: describe the nuclear fission of uranium-235. What are the products, and what is released that enables a chain reaction?
- Critical mass: what is critical mass, and why is it important in nuclear reactor design? What controls the chain reaction in a reactor?
- Energy comparison: the video discusses the energy released per fission event. Compare this (in principle) to the energy from burning the same mass of chemical fuel — which is greater, and by roughly how much?
🗣️ 3. After Viewing & Kaiako Move (Process & Apply)
Kaiako Move: Connect stellar fusion to Ernest Rutherford's pioneering nuclear splitting experiments in Aotearoa and Cavendish laboratories.
Immediate Task: Complete Section 6 of your Physics Portfolio: Fission & Fusion Energy Yield Reaction Calculations.
⚡ Whakaoho | Do Now: Modern Physics Recall (10 mins)
Splitting releases energy. So does joining. Both cannot be generally true.
Two minutes: use the curve you read last lesson. State the condition under which splitting releases energy, and the condition under which joining does. One sentence each, both referring to iron. If you can do that, you understand why stars fuse hydrogen but not iron.
📖 Activity 1: Physics Concept Exploration & Problem Solving (25 mins)
Balance and calculate (15 min). Balance a U-235 fission equation and a deuterium–tritium fusion equation — nucleon number and charge must both balance. Then calculate the energy released by each from the mass difference, and compare energy released per kilogram of fuel.
Why fusion is hard (10 min). Both nuclei in a fusion reaction are positive. Explain what must be overcome, why stars manage it and terrestrial reactors struggle, and what 'critical mass' means for a fission chain reaction by contrast.
📝 Activity 2: Level 3 Physics Portfolio Task & Merit/Excellence Scaffolding (20 mins)
Portfolio — Section 6. Submit: (1) both balanced equations with nucleon and charge checks shown; (2) energy-release calculations with a per-kilogram comparison; (3) a paragraph contrasting the practical barriers to fission and fusion, referring to the Coulomb barrier and critical mass.
🏫 Kaiako Planning & Pedagogy Notes
NCEA Level 3 Alignment: Direct preparation for Level 3 Physics (Demonstrate understanding of application of modern physics). Emphasise clear physical explanations and multi-step mathematical working for Merit/Excellence grades.