Lesson Plan

• Describe how wavelength influences the amount of diffraction at an edge or slit.
• Explain the relationship between wavelength, obstacle size, and diffraction angle.
• Predict diffraction behaviour for long, intermediate, and short wavelengths.
• Apply the concept to real‑world examples such as communication, optics, and acoustics.
• Analyse simple diffraction diagrams to identify strong versus weak diffraction.

• Projector and screen
• Whiteboard and markers
• Laser pointer with adjustable slit apparatus
• Ruler or measuring tape
• Printed worksheet with diagrams and questions
• Calculator
• Exit‑ticket cards

Begin with a quick question: “Why can you still listen to a radio station even when a building blocks the line of sight?” This activates prior knowledge of waves and wavelength. Remind students that they already know the basic definitions of wavelength and wave speed. State that by the end of the lesson they will be able to describe and predict how wavelength changes diffraction at an edge.

1. Do‑now (5'): Students answer a short prompt on everyday diffraction (radio vs light) and share responses.
2. Mini‑lecture (10'): Explain diffraction, introduce the λ‑to‑a ratio, and show the equation a sin θ = mλ with visual aids.
3. Demonstration (15'): Use a laser‑slit setup to compare a long‑wavelength (red laser) and a short‑wavelength (green LED) passing through the same slit; students record the spread angles.
4. Guided practice (10'): Complete a worksheet that asks students to fill a table matching wavelength categories to diffraction behaviour.
5. Application discussion (10'): In small groups, students discuss real‑world examples (communication, optics, acoustics) and present one example to the class.
6. Check for understanding (5'): Quick quiz (e.g., Kahoot or show‑of‑hands) on key concepts.

Summarise that longer wavelengths diffract more strongly because they are comparable to the size of obstacles, whereas short wavelengths travel almost straight. Students complete an exit ticket stating one practical implication of diffraction. For homework, ask them to research a technology that relies on long‑wave diffraction (e.g., AM radio or low‑frequency sonar) and prepare a short paragraph.