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Ripples squeeze through a gap. Do they fan out or go straight?
Diffraction Patterns lab · Last updated: 16 October 2026
Ripples roll across a tank towards a wall with a gap in it. You change the size of the gap and the length of the waves, then watch what comes through: a narrow beam, or a wide fan of curved ripples?
What you'll discover
- Waves spread out after passing through a gap or round an edge; this is diffraction.
- Spreading is greatest when the gap is about the same size as the wavelength.
- A wide gap compared with the wavelength lets waves pass almost straight through.
The science in plain words
Waves do not always travel in straight lines. When ripples pass through a gap, the parts near the edges spread sideways into the space behind the wall. This spreading is called diffraction, and it happens to every kind of wave: water, sound, light and radio.
How much a wave spreads depends on the size of the gap compared with the wavelength, the distance from one crest to the next. If the gap is about as wide as one wavelength, the waves fan out into neat semicircles. If the gap is many wavelengths wide, most of the wave passes straight through and only the edges bend a little.
This explains an everyday puzzle. You can hear someone talking round a corner but you cannot see them. Sound waves are tens of centimetres to metres long, similar to doorways, so they spread round easily. Light waves are less than a thousandth of a millimetre long, so through a doorway they barely diffract at all.
Diffraction of light can be seen with very narrow slits, and it limits how much detail a microscope or telescope can show.
Where it fits
- India, NCERT: Diffraction goes beyond the NCERT syllabus for classes 6 to 10; it builds on waves in Class 9 Chapter 11: Sound.
- United States: Grades 9 to 12
Common questions
What is diffraction in simple words?
Diffraction is the spreading of a wave when it passes through a gap or round an obstacle. Ripples fanning out behind a harbour entrance are a good example.
Why can we hear round corners but not see round them?
Sound waves are long, similar in size to doorways, so they spread round corners easily. Light waves are tiny, so they hardly spread through a doorway and travel almost straight.
When is diffraction strongest?
When the gap is roughly the same width as the wavelength of the wave. Much wider gaps let the wave pass through with only slight spreading at the edges.
Related labs
- Wave Interference: Two dippers, one duck. Where do the waves add up, and where do they cancel?
- Wave Reflection: Ripples hit a tilted wall. Which way do they bounce?
- Wave Motion: Shake one end of a cord. How fast does the wave run, and how long is each wave?
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Try it yourself
The Diffraction Patterns lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.