Mistake Master
Mistake Master · AP Physics 2 · Unit 14 · Step-Through Animation
Count the Shifts, Then Write It
You'll learnwhy a soap film shows colours and goes black as it drains: trace the path, convert the wavelength into the film, and count the reflection flips before writing anything.
A colourless soap film shows bands of colour, and just before it bursts the top goes black. Two reflections, added, explain both. Eleven short steps; press Next for each one.
twice the thickness · the wavelength in the film · count the reflection shifts
Before you start
What you're looking at
A thin soap film in cross-section, with the ray that reflects off the top and the ray that crosses the film and comes back out.
The question
Why does a colourless film show colours, and why does it go black as it drains?
Step 1 / 11