Wave mechanics: ripple tank and interference

A live ripple tank solves the wave equation as you watch. Click to drop oscillating sources, add a barrier with one or two slits, and see interference and diffraction form. Two more views show Young’s double slit with its fringe pattern and the normal modes of a vibrating membrane.

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What you can explore

Ripple tank

A water surface computed with a finite-difference solver, rendered with realistic caustics. Click to place up to five sources, then switch to a single or double slit barrier to watch the waves diffract and interfere behind it.

Double slit

Straight waves from a paddle reach two slits; behind them, two circular wavelets overlap. Calm lines fan out where they cancel and a screen on the far side glows with the bright and dark fringes, spaced λL/d apart.

Normal modes

A square drum skin vibrating in its natural modes, with nodal lines where the membrane never moves. Step through the modes to see how the patterns get more intricate as the frequency rises.

Key equations

  • ∂²u/∂t² = c² ∇²u
  • Δy = λL / d
  • path difference = mλ (bright), (m + ½)λ (dark)

Curriculum

AQA A-level physics 3.3.1–3.3.2, IB Physics C.2–C.3.

Common questions

Why does a double slit produce fringes?

Waves from the two slits travel different distances to each point. Where the path difference is a whole number of wavelengths they add up; where it is a half-wavelength out they cancel.

What is diffraction?

The spreading of a wave as it passes through a gap or around an edge. It is strongest when the gap is about the same size as the wavelength.

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