Lesson Plan

• Describe the law of reflection and identify conditions for reflection at a plane surface.
• Explain Snell’s law and predict the change in direction and wavelength when a wave refracts between media.
• Illustrate how diffraction occurs when a wave encounters a gap comparable to its wavelength and describe the resulting spreading.
• Compare and contrast reflection, refraction, and diffraction using real‑world examples.

• Projector and screen for diagrams
• Whiteboard and markers
• Printed worksheets with practice problems
• Laser pointer or ray‑box demonstration set
• Ripple tank or water tray with slits (optional)
• Rulers and protractors
• Exit ticket cards

Begin with a quick demonstration: shine a laser onto a flat mirror and observe the reflected beam. Ask students to recall how they have seen reflections in everyday life and what they expect to happen when the beam meets a different medium. Explain that today they will investigate three ways waves change direction—reflection, refraction, and diffraction—and that they will be able to predict the outcome using simple rules.

1. Do‑now (5’) – Short recall quiz on wave terms (incident, normal, wavelength); teacher checks answers.
2. Mini‑lecture (10’) – Present the law of reflection with diagram; emphasize angle equality and unchanged speed.
3. Guided demonstration (8’) – Use laser and mirror; students measure incident and reflected angles with a protractor.
4. Mini‑lecture (10’) – Introduce refraction, derive Snell’s law, show light entering a water tank; discuss constant frequency.
5. Interactive activity (12’) – Students predict ray paths in different media using provided diagrams; peer‑check.
6. Demonstration (8’) – Diffraction demo with ripple tank or laser through a narrow slit; observe spreading pattern.
7. Consolidation worksheet (12’) – Solve mixed problems on all three phenomena; teacher circulates for misconceptions.
8. Check for understanding (5’) – Exit ticket: one sentence describing each phenomenon.

Summarise that reflection keeps speed and frequency constant, refraction changes direction and wavelength while frequency stays the same, and diffraction spreads a wave when the aperture is comparable to its wavelength. Ask students to write one key fact about each on an exit ticket. For homework, assign practice questions from the textbook and encourage students to find a real‑world example of diffraction.