| Lesson Plan |
| Grade: Year 12 |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: define the specific acoustic impedance of a medium as Z = ρc, where c is the speed of sound in the medium |
Learning Objective/s:
- Define specific acoustic impedance and write the formula Z = ρc.
- Explain how impedance differences cause reflection and transmission of ultrasound at material boundaries.
- Calculate the impedance of a given medium and the intensity reflection coefficient for an interface.
- Describe the main types of ultrasound transducers and their role in impedance matching.
- Evaluate why a coupling gel is required for effective medical imaging.
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Materials Needed:
- Projector or interactive whiteboard
- PowerPoint slides with diagrams of transducers and impedance tables
- Handout containing typical acoustic impedances
- Scientific calculators or spreadsheet software
- Sample ultrasound coupling gel (demonstration)
- Physical model of a piezoelectric transducer (optional)
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Introduction:
Imagine being able to see inside the human body without making an incision. You already know that wave speed depends on a material’s density; today you will link those ideas to the concept of acoustic impedance. By the end of the lesson you will be able to define Z, calculate it for different media, and explain why matching impedances is crucial for clear ultrasound images.
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Lesson Structure:
- Do‑Now (5') – Quick quiz on the relationship between density, speed of sound, and wave speed.
- Mini‑lecture (10') – Introduce ultrasound frequencies, applications, and the formula Z = ρc.
- Demonstration (8') – Show a piezoelectric transducer and apply coupling gel; discuss impedance mismatch.
- Guided practice (12') – Calculate Z for water, muscle, and bone; compute the reflection coefficient at a tissue‑bone interface.
- Group activity (10') – Use the impedance table to predict image quality for different materials and present findings.
- Check for understanding (5') – Exit ticket: write one sentence explaining why a coupling gel improves image quality.
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Conclusion:
We reviewed the definition of specific acoustic impedance, practiced calculations, and saw how impedance matching enhances ultrasound performance. Collect the exit tickets to gauge understanding, and for homework complete a worksheet calculating Z and reflection coefficients for three additional materials of your choice.
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