8.2 Diffraction

Diffraction is the bending or spreading of waves around an obstacle or through an opening. It is most noticeable when aperture size is comparable to wavelength.

Compare aperture width with λ: narrower gaps produce broader spreading, while much larger gaps give weaker edge effects.

Water waves spread strongly through a gap about one wavelength wide but remain nearly straight through a gap many wavelengths wide.

Diffraction is not refraction: no change of medium is required, and the wave speed need not change.

In a diffraction experiment, observe the angular spread or fringe pattern while varying slit width or wavelength; larger λ or smaller slit gives more spreading.

Keep source, detector and geometry controlled, and compare the pattern qualitatively unless a quantitative model is required.

A laser through a narrower slit produces a wider central maximum than through a wider slit, while colour-dependent wavelength changes the spread.

A wider central maximum does not mean the waves travelled faster; it reflects the geometry-to-wavelength ratio.