Capacitor Lab sim. The first activity I wrote, 'Lectronic Plates, focused on the nature of the uniform electric field between two oppositely charged parallel plates. (The title was a mashup between tectonic plates and Lectric Shave. I might drop that opening apostrophe in future revisions.)
The new activity, The Two-Plate Special, is substantially more sweeping in its scope. It replaces a lengthy Springboard on capacitors that I thought was pretty comprehensive and well-designed when I wrote it.
The new activity was written in two parts. The first focuses capacitance: its meaning and how it varies with the configuration of the parallel plates.
The second part focuses on the energy-storing abilities of capacitors. Students are also asked to confront some apparent paradoxes that can be played out in the sim.
And that's one element of the fun you have authoring a PhET activity: messing around with the variables and finding puzzles. (And solving them, too!)
In this case, it was seeing how the behavior of the capacitor seemed to change depending on whether it was connected to a voltage source (battery) or the plates were isolated and the plate charge were manipulated.
Having read the activity guidelines written by the good people of PhET, I fear I might run afoul of their intentions. My activities may well provide too much guidance and not enough open-ended exploration.
My defenses include my status as a classroom teacher whose students don't enter the room brimming with curiosity for the topic of the day's lesson. I have great students; don't get me wrong. But they're teenagers, and thus have many distractions vying for their attention. I also work under the stricture of a school-year with a finite number of days. There is also my youthful inexperience: someday I might write activities that conform to PhET's hopes. When I am older and wiser. Time will tell.
The complete list of my PhET activities can be found on my PhET page.