Soap Bubbles & Oil Slicks

Colours from thin films

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

• Reflections from the two surfaces of a thin film interfere.
• Reflection from a denser medium adds a half-wavelength flip.
• A quarter-wave coating ($t = \lambda/4n$) cancels reflections.

Steps

1. Two reflections
2. Thickness and colour
3. Anti-reflection coating
4. The thinnest bright film
5. Black before it bursts
6. Blue without pigment