Double-Slit Interference Simulator
How to use the double-slit simulator
- Plane waves arrive from the near edge, pass through the two gaps in the barrier and spread out as two sets of circular waves.
- Where crests meet crests the water rises high; where a crest meets a trough it stays flat. The bars at the far edge show the resulting bright and dark fringes.
- Shorten the wavelength or widen the slits to pack the fringes closer together, as the formula Δy = λL ÷ d predicts.
Frequently asked questions
What does the double-slit experiment show?
That waves passing through two openings interfere: they add up in some directions and cancel in others, giving a pattern of bright and dark fringes. Young used it in 1801 to show light is a wave, and it works for electrons and atoms too, which is one of the foundations of quantum mechanics.
Where are the bright fringes?
At angles where the two paths differ by a whole number of wavelengths: d sin θ = mλ. On a screen at distance L, the fringes are Δy = λL ÷ d apart, so narrower slit spacing or longer wavelength spreads them out.
Why do the fringes fade towards the edges?
The wave from each slit gets weaker with distance, and the bars show a time average of the combined wave height, so the outer fringes carry less energy. With real light, the width of each slit also fades the pattern (single-slit diffraction).
It says WebGL is turned off.
The 3D view needs WebGL, which every current browser has. It can be switched off by hardware acceleration being disabled in the browser settings, or by a very old graphics driver. Turn hardware acceleration on, or try another browser.
Is anything uploaded?
No. The simulation is drawn by your own browser with WebGL; nothing is sent anywhere, and it keeps working offline once the page has loaded.