Physics
Waves and interference
Make circular ripples on water, watch two waves add up and send a plane wave through a slit.
Launch simulationHow it works
The simulation solves the two-dimensional wave equation: every point of the surface oscillates and passes its displacement on to its neighbours. The wavelength λ is the distance between neighbouring crests and λ = v / f; with the default values (2.0 m/s and 1.2 Hz) it is about 1.67 m. When two waves meet, their displacements add. Where crest meets crest, the wave grows; where crest meets trough, it cancels. Behind a narrow slit the wave spreads sideways; this is diffraction.
v = λ · freinforcement: Δd = k·λcancellation: Δd = (k + ½)·λ
Try it yourself
- Choose “One source”. Read the wavelength below the v = λ · f formula, then raise “Frequency” to 2.4 Hz. Predict first: the wavelength halves.
- Switch to “Interference” and find the calm bands where the waves cancel. Increase the frequency: the bands multiply and move closer together.
- Choose “Single slit” and lower the frequency to 0.6 Hz. A longer wave spreads more behind the opening. Widen the opening with the “Eraser” and compare.
- “Double slit” combines both effects: two openings produce an interference pattern, just like Young’s experiment with light.
Model limitations
This is a linear small-amplitude model on a grid with 0.1 m spacing. It ignores water flow and the fact that real water waves change speed with depth and wavelength. Very short waves (high frequency at low speed) are only approximated by the grid. Absorbing edges damp reflections; reflecting edges act like a wall.