Cambridge IGCSE Physics · Syllabus 0625 · Waves
Diffraction
What is Diffraction?
Diffraction is the spreading of a wave as it passes through a gap or travels past an edge. The wavelength, frequency and speed are unchanged; only the shape of the wavefronts changes. How much the wave spreads, and what that depends on, is Supplement 3.1.9 and 3.1.10.
This definition is part of the Waves chapter in Cambridge IGCSE Physics.
Common mistakes with Diffraction
- 6. “Diffraction is greatest through a very wide gap.” Supplement 3.1.9 Why wrongIt confuses how much energy gets through with how much the wave spreads. A wide gap passes plenty of energy, almost straight on. CorrectSpreading depends on the ratio of wavelength to gap width and is greatest when the gap is comparable to the wavelength. Say this“Diffraction is most noticeable when the gap width is about the same as the wavelength.” CheckWaves of wavelength 2 cm meet a gap. Which gives more spreading, 2 cm or 20 cm?