| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: understand that annihilation occurs when a particle interacts with its antiparticle and that mass–energy and momentum are conserved in the process |
Learning Objective/s:
- Describe the process of electron‑positron annihilation and the resulting photon emission.
- Explain how conservation of energy and momentum governs the energies and directions of the annihilation photons.
- Apply the annihilation concept to calculate photon energies for given kinetic energies.
- Relate annihilation photons to real‑world applications such as PET imaging.
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Materials Needed:
- Projector and screen
- PowerPoint/Google Slides presentation
- Printed worksheet with calculation problems
- PhET “Particle Interactions” simulation (or similar)
- Sample PET scan images (handout)
- Scientific calculators
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Introduction:
Begin with the striking question, “What happens when a particle meets its mirror image?” Students recall their knowledge of electrons, positrons, and the basic conservation laws. Explain that today they will see how these ideas predict the creation of two 511 keV photons and why this matters for technologies like PET scans.
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Lesson Structure:
- Do‑Now (5 '): Quick quiz on energy and momentum conservation from previous lessons.
- Mini‑lecture (10 '): Present the annihilation process, derive the two‑photon result, and discuss the 511 keV energy.
- Simulation activity (10 '): Students use the PhET simulation to vary positron kinetic energy and record photon energies and angles.
- Guided worksheet (15 '): Solve problems calculating photon energies for different initial kinetic energies and verify momentum balance.
- Application discussion (5 '): Examine PET scan images and connect the physics to medical imaging.
- Exit ticket (5 '): One‑sentence answer to “Why must at least two photons be produced in annihilation?”
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Conclusion:
Summarise that electron‑positron annihilation converts rest‑mass energy into photons while strictly conserving energy and momentum, typically producing two opposite‑direction 511 keV photons. Students hand in their exit tickets and receive a brief homework task: complete the remaining worksheet problems and read a short article on PET imaging to reinforce the real‑world link.
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