| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: calculate the energy of the gamma-ray photons emitted during the annihilation of an electron-positron pair |
Learning Objective/s:
- Describe the annihilation process of an electron‑positron pair and why it produces gamma‑ray photons.
- Calculate the rest‑mass energy of an electron and convert it between joules and electron‑volts.
- Apply the relation E = mₑc² to determine the energy of each photon emitted in the annihilation.
- Identify common errors in unit conversion and photon‑count reasoning.
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Materials Needed:
- Projector or interactive whiteboard
- Slides with equations and diagrams
- Scientific calculator for unit conversions
- Worksheet with worked example and practice problems
- Handout of physical constants table
- Exit‑ticket cards
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Introduction:
Begin with a quick question: What type of radiation is produced when matter meets antimatter? Review students' prior knowledge of mass‑energy equivalence (E = mc²) and the electron rest‑mass value. Explain that by the end of the lesson they will be able to calculate the energy of the gamma‑ray photons from electron‑positron annihilation and check their work using unit conversion.
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Lesson Structure:
- Do‑now (5'): Students answer a recall question on E = mc²; teacher checks responses.
- Mini‑lecture (10'): Explain annihilation, derive E_total = 2mₑc² and E_γ = mₑc²; display constants table.
- Guided practice (12'): Work through the full example on the board, converting joules to keV together.
- Independent practice (10'): Students complete worksheet problems, including a case with additional kinetic energy.
- Concept check (8'): Quick clicker poll addressing common pitfalls (single photon, unit mix‑up).
- Summary & reflection (5'): Recap key points; students write one takeaway on an exit ticket.
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Conclusion:
Summarise that each annihilation photon carries 511 keV, reinforcing the link between rest‑mass energy and gamma‑ray production. Ask students to record the calculation on an exit ticket as retrieval practice. For homework, assign problems that require converting between joules and electron‑volts for different particle masses.
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