Wave Effects

Overview

This lesson moves from wave vocabulary to wave behaviour. Keep every explanation tied to a wavefront diagram so students can see what changes at a boundary and what stays the same.

Key knowledge and explanations

• Show reflection at a plane barrier using parallel wavefronts and a normal line.
• Model refraction as a change in speed that changes wavelength when water depth changes.
• Use narrow gaps and edges in a ripple tank to show diffraction clearly.
• Compare large and small gaps against the same wavelength so students can judge when spreading is greatest.

Lesson flow

1. Begin with a retrieval task on wavelength, frequency, and wave speed so students can describe what they see in the ripple tank accurately.
2. Demonstrate reflection and refraction in the ripple tank, pausing to sketch the matching wavefront diagrams with students.
3. Compare diffraction through different gap widths and around an edge, then ask students to predict the pattern before each demonstration.
4. End with short explanation questions where students justify the pattern rather than only naming the effect.

Checks for understanding

• Ask which quantities change when waves enter shallower water: speed, wavelength, frequency, or all three.
• Use a quick comparison task where students rank three gaps by the amount of diffraction for the same wavelength.

Common mistakes or misconceptions

• Students often think refraction happens because waves hit a boundary rather than because their speed changes. Keep returning to the change in depth and wavefront spacing.
• Many assume the narrowest gap always gives the biggest pattern without relating it to wavelength. Use side-by-side diagrams with the same wavelength.
• Diffraction is sometimes treated as only a gap effect. Include diffraction at an edge explicitly.

Follow-up

• Set annotated wavefront diagrams for reflection, refraction, and diffraction as the main homework.
• Carry forward the language of longitudinal versus transverse waves, because the next lesson applies it to sound.