Your privacy choices

KiwiBee uses optional Google Analytics, Google Ads, and Meta Pixel cookies to understand adult visitors, measure completed sign-ups, and improve campaigns. Essential cookies always stay on. OpenAI’s ChatGPT Ads Pixel also measures page views and completed enquiries after advertising consent, and may use hashed contact details for matching. Privacy policy

Skip to main content

Double-Slit Interference

About this simulation

Double-Slit Interference models light of 400 to 700 nanometers passing two slits, with a screen 2.0 meters away and slits 0.04 millimeters wide. Students change the wavelength and the slit separation, and a tall intensity curve above the screen shows the pattern. Readouts give the fringe spacing, the first dark fringe and the number of bright fringes. It shows the wave nature of light and lets students test the relation that fringe spacing equals wavelength times screen distance over slit separation.

What students can explore

  • Change Wavelength from 400 to 700 nm and watch Fringe spacing grow.
  • Increase Slit separation and see the fringes pack closer together.
  • Read the First dark fringe position and explain why it is dark.
  • Count the Bright fringes on screen at two different separations.
  • Predict the spacing for a new setting, then check the readout.

Learning objectives

  1. 1Explain how overlapping waves produce bright and dark fringes.
  2. 2Use fringe spacing equals lambda L over d to predict patterns.
  3. 3Describe how wavelength affects fringe spacing.
  4. 4Explain why the experiment supports the wave model of light.

Questions teachers ask

Is the Double-Slit simulation free?

Yes. It is free, requires no sign-up and runs in any modern browser, including classroom whiteboards and tablets.

Why are there bright and dark fringes?

Waves from the two slits travel different distances to each point. Where the difference is a whole number of wavelengths they add and the screen is bright; at half a wavelength they cancel and it is dark.

How do I use it?

Use the wavelength and slit separation sliders, then read the fringe spacing and the number of bright fringes. Scene sizes are not to scale, but the readouts are real.

Which color gives wider fringes?

Red light, with the longest wavelength, gives wider fringe spacing than blue or violet light, since spacing is proportional to wavelength.

Embed this simulation

Drop it into your LMS, blog, or class site — free.

<iframe src="https://kiwibee.io/en/simulations/double-slit-3d-simulation/embed" title="Double-Slit Interference | KiwiBee" loading="lazy" allowfullscreen style="width:100%;height:min(70vh,620px);min-height:420px;border:0;border-radius:16px"></iframe>

Continue exploring

More interactive science models

Bring interactive science into your classroom

KiwiBee's free teacher workspace brings lesson planning, worksheets, classroom tools, and gradebook together in one place.

Start free and create your first class

or explore the teacher workspace →