Virtual ripple tank
The ripple tank is the classic school demonstration of wave behaviour. This one solves the wave equation as you watch, so you can add sources and barriers anywhere and see exactly how the waves respond.
Interactive, free and runs in your browser. Part of the Wave Mechanics simulations.
What you will see
A tank of water lit from above, with bright caustics where crests focus the light. Click to drop up to five oscillating dippers. Add a barrier with one slit to see diffraction spread the wave, or two slits to see the waves from each gap interfere into calm and rough bands.
Try this
- Place two sources close together and look for the calm nodal lines between them.
- Switch on the single slit and watch the wave spread out behind the gap.
- Switch to the double slit and compare its pattern with two point sources.
Common misconception
Interference does not destroy energy. Where waves cancel the water stays calm, but the energy is redistributed into the places where they reinforce.
Exam-style question
Two coherent sources produce waves of wavelength 1.0 cm. At a point P the path difference is 2.5 cm. Is P a place of constructive or destructive interference?
2.5 cm = 2.5λ, which is (m + ½)λ with m = 2, so the waves arrive half a cycle out of step: destructive interference, a calm point on a nodal line.
Key equations
∂²u/∂t² = c²∇²upath difference = mλ (constructive), (m + ½)λ (destructive)
Curriculum
AQA A-level physics 3.3.1–3.3.2, IB Physics C.2–C.3.