Explore the Double Slit & Diffraction
Change wavelength and slit spacing and see the interference pattern and its intensity graph. Free, no signup, runs in your browser.
- Free to use
- No signup
- Nothing to install
- Runs in your browser
Illustration. Open the tool for the real thing.
See it in action
The Double Slit & Diffraction with sample data entered and the result showing.
What is the Double Slit & Diffraction?
Change wavelength and slit spacing and see the interference pattern and its intensity graph. It runs in your browser, so a change to a setting or a drag on an object shows up at once.
Interference from two slits proved that light is a wave and later that electrons behave like waves too. The same ideas drive interferometers and holography.
3 steps to your result
Open the tool and follow along. Nothing to install.
What you get
Bright fringes occur where the path difference is a whole number of wavelengths: d sin θ = mλ.
Fringe spacing is Δy = λL / d.
Narrower slits spread the light out more (diffraction envelope).
Change the colour of the light and watch the fringes move.
Drag the slits closer together and see the pattern widen.
Make each slit wider and watch the pattern fade away from the centre.
Used for
Pick one to see how it fits.
Physics learners
Physics students in middle school, high school and first-year university, teachers who want a quick demonstration for the projector, and anyone revising for exams.
Try it freeTeachers
For teachers: project the Double Slit & Diffraction on the board, let students predict the result, then run it together and test this: Drag the slits closer together and see the pattern widen. For students: change one thing at a time and write down what changes.
Try it freeHow it compares
A plain look at this tool next to the usual alternative.
| This simulation | Textbook diagram | |
|---|---|---|
| Interactive | Drag, tap and change settings | Fixed picture |
| Install | Nothing to install | Not needed |
| Cost | Free to use | Depends on the book |
Questions people ask
Why do we see bright and dark bands?
Light from the two slits overlaps. Where crests meet crests the waves reinforce (bright). Where crests meet troughs they cancel (dark).
What happens if you make the slits closer together?
The fringes spread further apart, because fringe spacing is inversely proportional to the slit separation.
Is the Double Slit & Diffraction free to use?
Yes. The Double Slit & Diffraction is free, needs no signup or download and runs in your web browser. It is part of the Physics group of AZRS simulations.
Does the Double Slit & Diffraction work on a phone or tablet?
Yes. The Double Slit & Diffraction takes touch input as well as mouse input, so you can use its 3 adjustable settings with a finger. A larger screen makes the controls and graphs easier to read.
How do I use the Double Slit & Diffraction?
1. In the Double Slit & Diffraction, use the controls to change Wavelength, Slit separation d, Slit width a. The simulation reacts instantly. 2. In the Double Slit & Diffraction, pick an option such as Wave, Particles to switch modes or load an example. 3. In the Double Slit & Diffraction, press "Clear screen" to start, reset or change what is happening. 4. Start with this experiment: Change the colour of the light and watch the fringes move. Drag any glowing handle, object or slider with your mouse or finger and the Double Slit & Diffraction responds in real time. 5. Change one setting at a time and watch which readout moves, then compare it with this idea: Bright fringes occur where the path difference is a whole number of wavelengths: d sin θ = mλ.
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Try the Double Slit & Diffraction now
Change wavelength and slit spacing and see the interference pattern and its intensity. Free to use.
Try it free