Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Physics
Lesson Topic: use Wien’s displacement law and the Stefan–Boltzmann law to estimate the radius of a star
Learning Objective/s:
  • State Wien’s displacement law and the Stefan–Boltzmann law.
  • Derive the formula for a star’s radius in terms of its luminosity and effective temperature.
  • Apply the derived formula to calculate stellar radii from given λmax and luminosity data.
  • Interpret how temperature influences radius for a fixed luminosity.
Materials Needed:
  • Projector and screen
  • Whiteboard and markers
  • Scientific calculators or spreadsheet software
  • Printed worksheet with star data and constants
  • Formula sheet (Wien’s constant, σ, solar values)
  • Exit‑ticket slips
 Introduction:
Stars may look like point sources, yet physics lets us estimate their sizes. Students should already recall black‑body radiation and basic algebraic manipulation. Today they will demonstrate they can compute a star’s radius from its peak wavelength and luminosity and explain the temperature‑radius relationship.
Lesson Structure:
  1. Do‑now (5'): quick quiz on Wien’s law and the Stefan–Boltzmann law.
  2. Mini‑lecture (10'): derive R = √[L/(4πσT⁴)] and discuss each term.
  3. Guided example (10'): work through the Sun calculation step‑by‑step.
  4. Group activity (15'): using the worksheet, calculate radii for Betelgeuse and an exoplanet‑host star.
  5. Concept discussion (5'): compare results and relate temperature to radius.
  6. Check for understanding (5'): exit‑ticket question – “What happens to the radius if temperature doubles while luminosity stays constant?”
Conclusion:
We reviewed how Wien’s and Stefan–Boltzmann laws combine to give a practical radius estimate and applied it to real stars. Students now complete an exit ticket and are assigned three additional practice problems to reinforce the method at home.