| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: Describe redshift as an increase in the observed wavelength of electromagnetic radiation emitted from receding stars and galaxies |
Learning Objective/s:
- Describe redshift as an increase in observed wavelength from receding astronomical objects.
- Explain the relationship between redshift, recessional velocity, and Hubble’s law.
- Calculate redshift, velocity, and distance using the provided formulas.
- Identify and correct common misconceptions about redshift.
- Interpret spectral diagrams to determine the amount of redshift.
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Materials Needed:
- Projector and screen for slides
- Whiteboard and markers
- Printed worksheet with spectral‑line examples
- Calculator or classroom computers
- Online redshift simulation (optional)
- Reference chart of Hubble’s constant
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Introduction:
Begin with a short animation showing a galaxy’s light stretching as it moves away, linking to the Doppler effect students already know from sound waves. Ask learners to recall how motion affects frequency and wavelength, then state that today they will explore how this principle reveals the expanding Universe. Success will be demonstrated by correctly calculating redshift and using it to estimate a galaxy’s distance.
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Lesson Structure:
- Do‑now (5 '): Quick quiz on the Doppler effect for sound; brief discussion of answers.
- Mini‑lecture (10 '): Introduce Doppler effect for light, define redshift/blueshift, present the redshift formula.
- Guided example (12 '): Walk through the sample calculation (λ₀ = 500 nm, λ_obs = 510 nm) on the board while students complete the worksheet.
- Interactive simulation (8 '): Use an online redshift tool to vary velocity and observe spectral shifts; students record observations.
- Group activity (10 '): Teams calculate recessional velocity and distance for a given redshift (z = 0.1) using Hubble’s constant; teacher circulates to address misconceptions.
- Check for understanding (5 '): Exit‑ticket – one sentence explaining how redshift supports the Big Bang theory.
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Conclusion:
Summarise that redshift measures how light stretches with cosmic expansion, allowing us to infer velocities and distances of galaxies. Remind students to complete the worksheet problems for homework to reinforce the calculations. Collect exit tickets and ask them to review the misconceptions list before the next class.
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