Lesson Plan

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Lesson Plan
Grade: Date: 25/02/2026
Subject: Physics
Lesson Topic: show an understanding of experiments that demonstrate diffraction including the qualitative effect of the gap width relative to the wavelength of the wave; for example diffraction of water waves in a ripple tank
Learning Objective/s:
  • Describe the relationship between aperture size and wavelength on diffraction patterns.
  • Explain how gap width influences water‑wave diffraction in a ripple tank.
  • Predict diffraction outcomes for different a/λ ratios using qualitative reasoning.
  • Analyse experimental data from single‑slit, double‑slit, and ripple‑tank demonstrations.
  • Apply diffraction concepts to real‑world applications such as optical resolution.
Materials Needed:
  • Ripple tank with adjustable barrier/gap
  • Laser pointer and single‑slit apparatus
  • Double‑slit slide or diffraction grating
  • Screen or white paper for observing light patterns
  • Rulers or measuring tapes
  • Projector and slides of diffraction diagrams
  • Worksheets for data recording and analysis
 Introduction:
Begin with a striking video of water waves passing through a narrow opening, prompting students to predict what they will see. Review the concept that waves bend when encountering obstacles comparable to their wavelength. Explain that today’s success criteria are to articulate how gap width relative to λ shapes diffraction patterns and to interpret experimental observations.
Lesson Structure:
  1. Do‑now (5'): Students answer a quick question on wave‑obstacle interactions.
  2. Mini‑lecture (10'): Review diffraction theory and the a/λ relationship with slides.
  3. Demonstration 1 – Laser single‑slit (8'): Show the diffraction pattern and discuss the central maximum.
  4. Demonstration 2 – Ripple tank (12'): Vary gap widths (>>λ, ≈λ, <<λ) and have students record observations.
  5. Guided analysis (10'): Students compare observed patterns to predictions and complete a worksheet.
  6. Check for understanding (5'): Exit ticket – predict diffraction for a new aperture size.
Conclusion:
Elicit a brief recap of how aperture size governs diffraction, linking observations from both light and water experiments. Collect exit tickets and remind students to complete a homework worksheet that asks them to calculate expected angles for given slit widths. Highlight the relevance of diffraction limits in designing optical instruments.