Lesson Plan

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Lesson Plan
Grade: Date: 25/02/2026
Subject: Physics
Lesson Topic: understand that the lines in the emission and absorption spectra from distant objects show an increase in wavelength from their known values
Learning Objective/s:
  • Describe how red‑shift of spectral lines indicates an increase in wavelength relative to laboratory values.
  • Calculate radial velocity from observed and rest wavelengths using the Doppler formula.
  • Apply Hubble’s law to estimate the distance of an extragalactic object from its radial velocity.
  • Determine a star’s radius using the Stefan‑Boltzmann law given its luminosity and effective temperature.
Materials Needed:
  • Projector with slide deck
  • Spectral line data handout (rest & observed wavelengths)
  • Calculator or spreadsheet software
  • Whiteboard and markers
  • Worksheets for calculations
  • Access to an online spectral database (optional)
 Introduction:
Begin with a quick demonstration of a familiar emission line (e.g., hydrogen Hα) and ask students what they would expect to see if the source were moving away. Recall the Doppler effect for light and how wavelength shifts reveal motion. Explain that today they will use measured shifts to calculate radial velocities, distances, and ultimately stellar radii, with success measured by completing the worked example.
Lesson Structure:
  1. Do‑now (5 min): Short question on Doppler shift for sound vs. light to activate prior knowledge.
  2. Mini‑lecture (10 min): Review red‑shift, the Doppler formula, and Hubble’s law.
  3. Guided data analysis (15 min): Using the handout, calculate Δλ and vr for the three listed spectral lines.
  4. Group calculation (10 min): Apply Hubble’s law to estimate distance for one line and discuss assumptions.
  5. Radius determination (10 min): Compute stellar radius from given luminosity and effective temperature using the Stefan‑Boltzmann equation.
  6. Whole‑class discussion & check for understanding (5 min): Share results, address misconceptions, and answer questions.
Conclusion:
Recap how red‑shift leads to radial velocity, distance, and radius estimates, reinforcing the key equations. Students complete an exit ticket by writing one step they found most challenging. For homework, assign a new set of spectral data for students to analyse and report the calculated stellar radius.