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📘 Lesson 7 of 7 · Waves

🌈 Diffraction

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.

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01 Key Concepts

What is Diffraction?

The bending and spreading of waves as they pass through a narrow opening (aperture) or around the edge of an obstacle.

Diffraction 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.

Single-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.

Why 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.

Diffraction 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.

02 Solved Examples

Example 1 Why can you hear someone talking around the corner of a building, even though you can't see them?
  1. Sound waves have relatively long wavelengths (often meters), comparable to or larger than typical obstacles like building corners.
  2. This causes sound to diffract (bend) noticeably around the corner, reaching your ears even without a direct line of sight.
  3. Visible light has a much shorter wavelength and diffracts far less around large obstacles like buildings.
Answer: Sound's long wavelength diffracts significantly around obstacles, while light's much shorter wavelength does not diffract as noticeably
Example 2 Why does diffraction become more noticeable when a wave passes through a very narrow slit?
  1. Diffraction effects are strongest when the opening's size is comparable to or smaller than the wavelength.
  2. A narrower slit makes this condition more likely to be met, producing more pronounced spreading.
Answer: A narrower opening relative to the wavelength produces more pronounced diffraction (spreading) of the wave
Example 3 What tool uses diffraction to break light apart into its component wavelengths for analysis?
  1. A specific optical device with many closely spaced slits is designed exactly for this purpose.
Answer: A diffraction grating

03 Practice Questions

1What is 'diffraction'?
The bending and spreading of waves around obstacles or through openings
2Does diffraction become more or less noticeable as wavelength increases (relative to the opening size)?
More noticeable
3Why 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
4What pattern does light produce when passing through a single narrow slit?
A bright central band with dimmer bands on either side
5What tool uses many closely spaced slits to diffract light into a spectrum?
A diffraction grating

📄 Diffraction — Downloadable Worksheet

10 questions with a full answer key. Grab the PDF to print, or try the interactive version in your browser.

🗒 Cheat Sheet ⬇ Download PDF 🖥 Interactive Worksheet