Wave Optics Lab

A ripple tank solving the 2D wave equation. Pick a preset, then click the tank to add sources, draw barriers or lenses, and watch interference and diffraction appear.

Simulation

Frequency Wave speed

Damping Sim speed

Presets

Sources

Source count Selected source

Freq × Phase Amplitude

Source speed (Doppler)

Slit screen

Number of slits

Slit width Separation

Draw tools

Brush size Medium speed

Display

Colormap Brightness

Source markers Detector plot

Measurements

Wavelength λ: —
Period T: —
Wave speed c: —
Fringe spacing, predicted: —
Fringe spacing, measured: —
Ruler: drag with the ruler tool
Doppler: source at rest

Lengths are in grid cells, time in steps. Place the ruler across several crests to measure λ yourself, and compare it with the value above.

What am I seeing?

Superposition. The wave equation is linear, so waves from different sources simply add. Where crests meet crests the result is bigger, where crests meet troughs they cancel.
Interference. Two sources in step give bright lines where the path difference is a whole number of wavelengths (d sin θ = mλ) and dark lines halfway between.
Diffraction. A slit of width a spreads a wave into an angle of about λ/a. The single-slit pattern has its first minimum at sin θ = λ/a. A grating of N slits sharpens the bright fringes of a double slit.
Huygens principle. Every point of a wavefront acts as a new source of circular wavelets. Cut a slit in a barrier and you see exactly one such wavelet. A zone plate blocks every second Fresnel zone so that the rest arrive in step and focus.
Refraction. In a slower medium the wavelength shrinks and fronts bend toward the normal (Snell’s law, sin θ₁ / sin θ₂ = v₁ / v₂). Going from slow to fast beyond the critical angle gives total internal reflection. A convex lens slows the middle of a plane wave more than the edges, so it focuses.
Doppler and Mach cone. A moving source squeezes the fronts ahead (λ(1 − M)) and stretches those behind (λ(1 + M)). Beyond M = 1 the fronts pile up into a cone with sin α = 1 / M.
Standing waves. Waves bouncing between walls interfere with themselves. At the resonant frequencies they form fixed patterns of nodes and antinodes.
Numerics: u_tt = c² ∇²u on a 320 × 220 grid, leapfrog time stepping, a damping sponge at the edges absorbs outgoing waves. Walls are fixed (u = 0). Fraunhofer theory is exact only far from the screen, so expect small differences.