I don't know why light slows down in water. (part 2)

Supported by Screen Australia and Youtube through the Skip Ahead initiative.

Links to the other videos mentioned:
Part 1 of this story: https://youtu.be/yP1kKN3ghOU
3Blue1Brown's explanation of Feynman's proof: https://www.youtube.com/watch?v=KTzGBJPuJwM

Experiment:
If you’d like to try the experiment I did at home then you’ll need a phone with Lidar or you can get a laser meter quite cheaply at a hardware store. If you use an iphone, the app I found most reliable for the measurement was this one: https://apps.apple.com/us/app/lidar-measuring/id1535032210

Code:
The 3D simulation is here: https://github.com/mithuna-y/speed_of_light_in_a_medium/tree/main/multiple_layers

References:
The Feynman lectures- “Ch 31: On the origin of refractive index” and “Ch 48: Beats”