Yesterday, I told them too much. I made the pattern with how the wavelength, frequency, and speed change when a wave enters a new medium. So they didn't really think about those problems; they played WTF again. (What's the formula rather than thinking.)
Today, after doing some whiteboarding, I wanted to try the interference pattern with overhead transparencies. But I hadn't had space in my brain to figure out the pattern of questioning I wanted to do, so it wasn't very coherent. I figured it out more by my afternoon period, but I still didn't feel good about. More interesting stuff tomorrow.