Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Physics
Lesson Topic: explain why redshift leads to the idea that the Universe is expanding
Learning Objective/s:
  • Describe how stellar radii are calculated using luminosity, temperature and distance.
  • Explain the concept of redshift and its relation to recession velocity.
  • Apply Hubble’s law to interpret redshift as evidence for cosmic expansion.
  • Analyse sample galaxy data to identify the linear redshift–distance relationship.
  • Connect accurate distance measurements from redshift to determining extragalactic stellar radii.
Materials Needed:
  • Projector and screen for slides/diagrams
  • Whiteboard and markers
  • Handout with redshift and Hubble diagram
  • Printed sample data table for each group
  • Calculator or spreadsheet software
  • Laser pointer for highlighting equations
 Introduction:
Begin with a quick poll: who can recall what happens to light when a source moves away? Review the Doppler effect for sound and link it to light. Explain that today’s success criteria are to explain redshift, use Hubble’s law, and connect these ideas to measuring stellar sizes.
Lesson Structure:
  1. Do‑now (5') – students answer a short question on Doppler shift on the whiteboard; teacher checks answers.
  2. Mini‑lecture (10') – present redshift definition, equations, and Hubble’s law with slides.
  3. Guided calculation (12') – work through the stellar radius formula, then use sample galaxy data to compute recession velocities and distances.
  4. Group activity (15') – analyse the provided data table, plot redshift vs distance on graph paper or a spreadsheet, and identify the linear trend.
  5. Concept discussion (8') – students summarise how the linear relation supports an expanding universe and why accurate distances matter for stellar radii.
  6. Quick check (5') – exit ticket: one sentence explaining why redshift implies expansion.
Conclusion:
Recap that redshift quantifies the stretching of light, Hubble’s law links it to distance, and the linear trend confirms universal expansion. Students submit an exit ticket stating the key idea. For homework, assign a worksheet converting redshift values to distances using Hubble’s constant.