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Waves · Quick Reference
Diffraction Cheat Sheet
In one line: diffraction is the bending and spreading of waves as they pass through openings or around obstacles — a uniquely wave-like behavior that lets sound bend around corners and light create intricate patterns.
Key Ideas
1What is Diffraction?. The bending and spreading of waves as they pass through a narrow opening (aperture) or around the edge of an obstacle.
2Diffraction and Wavelength. Diffraction effects are most noticeable when the size of the opening or obstacle is comparable to (or smaller than) the wave's wavelength -- longer wavelengths diffract more noticeably.
3Single-Slit Diffraction Pattern. Light passing through a single narrow slit produces a pattern with a bright central band and progressively dimmer bands on either side, due to interference between different parts of the wave passing through the slit.
4Why We Can Hear Around Corners but Not See Around Them. Sound has much longer wavelengths than visible light, so sound diffracts noticeably around everyday obstacles (like walls), while visible light's much shorter wavelength diffracts far less noticeably.
5Diffraction Gratings. A surface with many closely spaced slits or grooves that diffracts light into a detailed spectrum, used in spectroscopy to analyze light's exact wavelength composition.
Worked Examples
Why can you hear someone talking around the corner of a building, even though you can't see them?
Sound's long wavelength diffracts significantly around obstacles, while light's much shorter wavelength does not diffract as noticeably
Why does diffraction become more noticeable when a wave passes through a very narrow slit?
A narrower opening relative to the wavelength produces more pronounced diffraction (spreading) of the wave
What tool uses diffraction to break light apart into its component wavelengths for analysis?
A diffraction grating
Practice Yourself
What is 'diffraction'?
The bending and spreading of waves around obstacles or through openings
Does diffraction become more or less noticeable as wavelength increases (relative to the opening size)?
More noticeable
Why can sound bend around corners more easily than light?
Sound's much longer wavelength diffracts more noticeably around everyday-sized obstacles than light's short wavelength
What pattern does light produce when passing through a single narrow slit?
A bright central band with dimmer bands on either side