| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: use the expression fο = f sv / (v ± vs) for the observed frequency when a source of sound waves moves relative to a stationary observer |
Learning Objective/s:
- Describe the Doppler effect for sound and how source motion alters observed frequency.
- Apply the formula fₒ = (fₛ v)/(v ± vₛ) to calculate the observed frequency for approaching and receding sources.
- Choose the correct sign convention based on the direction of source motion.
- Solve numerical problems and interpret whether the pitch increases or decreases.
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Materials Needed:
- Projector with slides on the Doppler effect
- Speakers for audio demonstration of pitch change
- Printed worksheet with worked example and practice questions
- Scientific calculators
- Online Doppler simulation (e.g., PhET)
- Whiteboard and markers
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Introduction:
Begin with a quick think‑pair‑share on everyday sounds that change pitch, such as ambulance sirens. Review that students already know frequency and wave speed, linking this to the new concept of relative motion. State that by the end of the lesson they will be able to predict and calculate the observed frequency using a single formula.
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Lesson Structure:
- Do‑now (5'): Students list real‑world examples of the Doppler effect and discuss why pitch changes.
- Mini‑lecture (10'): Derive the formula for a moving source, highlight the “−” for approach and “+” for recession.
- Guided example (10'): Work through the police‑siren problem together, students fill in steps on their worksheet.
- Interactive simulation (10'): Use the PhET Doppler app; students vary source speed, record fₒ, and identify the pattern.
- Practice problems (10'): Students solve three provided questions, then peer‑check answers with the checklist.
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Conclusion:
Summarise the sign‑selection rule and the physical meaning of the calculated frequency shift. Ask each student to write one‑sentence exit ticket answering “When does the observed pitch increase?” Assign homework to complete two additional Doppler problems from the textbook.
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