Wavelength
80
Frequency
0.50
§ 06 · Sandbox · Wave optics
Filed 2026.05
Two speakers, one slit, and the geometry of agreement.
A room seen from above. Two sources hum at the same pitch and circular wavefronts spread from each. Where two crests arrive together you see a bright stripe; where a crest meets a trough, silence. Slide a wall in, pierce it once, then twice — and the famous fringes of the double-slit experiment appear on their own. Drag everything. Hold to freeze and look.
Mode Open room
λ 80 px
f 0.50 Hz
State ▶ live
Sources 2 coherent
Slits —
drag · sources or slits · press H to hold
Wall & slits
Slit width
22
Sources
View
Controls
Reading
Hover the room to read amplitude.
Notes from the workshop
§ 06 · ReadingA
Two coherent sources, same frequency. Each emits circular crests that fall off with distance like ripples on a pond.
B
Where the path differences are whole wavelengths the crests agree and you see bright lines. Where they differ by half, the wave cancels itself.
C
Drop in a wall with two narrow slits and you have rebuilt Thomas Young's 1801 experiment — the one that first told us light behaves like a wave.
D
Hold the field still (press H) and the fringe spacing becomes legible. Narrow the slits and the pattern smears out wider; widen them and it sharpens.
How it works
§ 06 · Method
Each pixel of the room samples a sum of sinusoids. For a source S and a receiver at
distance d, the field is sin(kd − ωt) / √d, with k = 2π/λ
and ω = 2πf. The square-root attenuation is the two-dimensional analogue of the
inverse-square law and keeps the picture honest near a source.
A wall, when present, is opaque except where you have cut slits. Past it, each open slit is treated as a fresh Huygens source — the path from speaker to receiver runs through one of the apertures, and we add the contributions from every open slit. This is the cleanest path to the familiar fringes without simulating a full wave-equation grid.
Bright cells are wave crests at the present instant, dark cells are troughs. The interference is not a render trick: shift either source by half a wavelength and watch a bright fringe slide precisely to where a dark one used to be.