| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: Describe the use of a ripple tank to show: (a) reflection at a plane surface (b) refraction due to a change in speed caused by a change in depth (c) diffraction due to a gap (d) diffraction due to an edge |
Learning Objective/s:
- Describe how a ripple tank demonstrates reflection, refraction, and diffraction of water waves.
- Explain the relationship between water depth, wave speed, and wavelength.
- Predict the direction of reflected and refracted wave fronts using the law of reflection and Snell’s law.
- Analyse diffraction patterns produced by a slit and a straight edge and relate them to Huygens’ principle.
- Record and interpret qualitative wave‑front sketches to support explanations.
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Materials Needed:
- Ripple tank with transparent sides and adjustable water depth.
- Wave generator/vibrator (low‑frequency source).
- Plane glass plate (reflecting barrier).
- Removable depth plate to create a step change.
- Rectangular slit of variable width.
- Thin straight metal edge.
- Overhead projector or digital camera for viewing patterns.
- Worksheet or lab notebook for sketches and observations.
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Introduction:
Begin with a short video of ocean waves reflecting off a pier to capture interest. Ask students what factors might change a wave’s direction or shape, linking to prior knowledge of reflection and refraction. Explain that today they will use a ripple tank to visualise these wave behaviours and that success will be measured by accurate sketches and explanations of each phenomenon.
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Lesson Structure:
- Do‑Now (5 minutes): Students answer quick questions on wave terminology in their notebooks.
- Demonstration set‑up (10 minutes): Teacher fills the tank, sets the depth, and explains safety while students observe the general procedure.
- Reflection activity (10 minutes): Show the plane glass plate, have students sketch incident and reflected fronts, then discuss the equality of incidence and reflection angles.
- Refraction & Diffraction stations (20 minutes): Small groups rotate through three stations—depth step (refraction), rectangular slit (gap diffraction), and straight edge (edge diffraction)—recording observations and calculating wavelength changes.
- Check for Understanding (5 minutes): Whole‑class concept‑mapping and a short exit ticket where each student describes one example of each phenomenon.
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Conclusion:
Recap the four wave phenomena observed and how the ripple tank illustrated the underlying principles. Students complete an exit ticket stating one real‑world application for each effect. Assign homework to research another wave demonstration (e.g., sound or light) and compare it with the ripple‑tank results.
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