Diffraction
Diffraction
- A wave does not always continue as a narrow straight beam. At a gap or an edge, it can spread into the region beyond.
- The important comparison is not “small gap” by itself. Compare the gap width with the wavelength.
See what the gap changes
straight wavesspread-out wavesDefinition
2 marksWhat is meant by diffraction?
Model answer: The spreading of a wave as it passes through a gap or around an edge.
gap = 3.0 λ·spread half-angle ≈ 19°·little diffraction
Compare gap width with wavelength
| Gap width compared with λ | What the wave does |
|---|---|
| much larger than λ | little spreading; wavefronts stay nearly straight |
| about the same as λ | the clearest strong spreading; broad circular wavefronts |
| smaller than λ | broad spreading, but less wave energy passes through |
- If the gap stays fixed, a longer wavelength gives more diffraction.
- This is why sound bends around a doorway far more noticeably than visible light: sound wavelengths are much closer to doorway size.
Your turn9702/23/M/J/25 Q6(a)
State what is meant by diffraction. [2] (9702/23/M/J/25 Q6(a))
Show worked answer
Diffraction is the spreading of a wave as it passes through an aperture or around an edge.