We played with double slits today. We had a small class, with lots of students out for robotics competitions and Football Hall of Fame field trips. So we made some qualitative observations, and they fit with our model of two sources we talked about yesterday. One student was very surprised. "Wait, so that model actually works?"
Yes. Yes it does.
"It means that light is a wave," said another student.
"Well, this model works for now," I replied. "Don't be so sure."
Then we derived the path length difference equation for a double slit. I did it too soon. I should have waited until we had a better understanding of path length difference, with simpler questions, before going into the complicated double slit derivation.