Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Physics
Lesson Topic: recall and use I = I0e–μx for the attenuation of X-rays in matter
Learning Objective/s:
  • Describe the production mechanisms of X‑rays (bremsstrahlung and characteristic radiation).
  • Explain the exponential attenuation law I = I₀ e⁻ᵘˣ and the factors that influence the coefficient μ.
  • Calculate the thickness of an absorber required to achieve a specified intensity reduction.
  • Interpret attenuation data (linear attenuation coefficients, HVL) for different materials.
  • Apply the attenuation concept to design simple shielding or filter choices.
Materials Needed:
  • Projector or interactive whiteboard
  • PowerPoint slides with X‑ray tube diagram and attenuation graphs
  • Handout containing the attenuation formula, sample data table, and practice problems
  • Calculator or spreadsheet for exponential calculations
  • Samples of absorber materials (e.g., aluminium and lead sheets) for demonstration (optional)
  • Whiteboard and markers
 Introduction:
Begin with a striking image of a modern CT scanner and ask students how the machine can see inside the body without opening it. Recall that X‑rays are produced by high‑energy electrons striking a metal target, a concept covered last week. Explain that today’s success criteria are to predict how much of an X‑ray beam is removed by different materials using the exponential attenuation law.
Lesson Structure:
  1. Do‑now (5’) – Quick clicker quiz on X‑ray production (bremsstrahlung vs. characteristic).
  2. Mini‑lecture (10’) – Derive I = I₀ e⁻ᵘˣ, define μ, discuss factors (photon energy, atomic number, density); show ln I vs. x graph.
  3. Guided example (12’) – Work through the aluminium thickness calculation (10 % intensity) on the board; students follow in notebooks.
  4. Data‑interpretation activity (10’) – Using a table of μ values, groups calculate HVL for lead and water and compare results.
  5. Practical demonstration (optional, 8’) – Video of intensity measurements before/after an aluminium sheet; discuss safety and observations.
  6. Check for understanding (5’) – Exit ticket: write the attenuation formula and one factor that increases μ.
  7. Homework brief (2’) – Assign worksheet with additional attenuation problems (lead and water thickness calculations).
Conclusion:
Summarise that X‑ray intensity drops exponentially with material thickness and that the linear attenuation coefficient captures material‑specific behaviour. Remind students to record the formula and a key factor affecting μ on their revision cards. For the exit ticket, they will submit one real‑world example of shielding design, and the homework will reinforce calculations for lead and water.