Young’s Double Slit

Proof that light is a wave

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Two slits produce bright and dark fringes: evidence that light is a wave.
• Bright fringes occur where the path difference is a whole number of wavelengths.
• Fringe spacing $\Delta y = \lambda L / d$.

Steps

1. Light plus light = darkness?
2. Fringe spacing
3. Tune the fringes
4. Red laser
5. Green fringes
6. One particle at a time