Ripple Tank (Wave Interference)

A ripple tank that solves the 2D wave equation ∂²u/∂t² = c² ∇²u with explicit finite differences (FDTD). Use it to see interference and single/double-slit diffraction build up in real time.

Modes

• Double slit / Single slit — a plane wave hits a reflecting barrier; waves diffract through the slit(s) and interfere.
• Two sources — two point sources in phase, producing classic interference fringes.
• Plane wave — an unobstructed travelling wavefront.

Controls: wavelength (in grid cells), slit separation and slit width (slit modes), simulation speed (steps per frame), and the intensity screen on the right edge (time-averaged |u|²), which shows the fringe pattern.

Physics: bright fringes (constructive interference) occur where the path difference is a whole number of wavelengths, d·sinθ = mλ. Larger slit separation → closer fringes; longer wavelength → wider fringes; a narrower slit → broader diffraction envelope.

Notes & limitations: barriers are perfectly reflecting; the outer border uses an absorbing sponge layer (small residual reflections remain); the Courant number is fixed below the stability limit, so a fixed c is used (wavelength sets the source period).