One day when we were getting the Van de Graaff generator out for some static electricity demos, one of my colleagues shared one of the coolest things I've seen. Rather than discharge the voltage build up through a finger or knuckle, he had students draw pictures on notecards using standard graphite pencils and held them up to the generator to create a path to ground through the graphite. The result is an impressive spark (larger build up with the greater gap) that followed the path drawn.
To try this out, I drew a simple lightning bolt zig zag on a piece of paper. Holding one end of the drawing firmly with my thumb, I then held up the other end of the graphite line while charging up the Van de Graaff. The result can be seen in the video that my colleague and I captured below. I think we should refer to this as "Van de Graaff-ite" ;)
If you capture it in slow-mo you can get pretty impressive frames showing exactly how the discharge is following the graphite! It's basically instantaneous and while you can see it in real time, there is just something special about seeing the path that electricity is taking
Troubleshooting
In my experience (and hearing from others who have tried) this demo doesn't always work on the first go. I am limited to the experience that I have with our equipment but here are the troubleshooting steps that are worth trying
Disclaimer
As with any Van de Graaff generator demonstration, it is important to understand the safety considerations. There are some great resources through Flinn and IOP.
Iterations
One of my favorite parts about Twitter is how easy it is to share and "remix" an idea. After sharing the video posted above several months ago, several other teacher have tried this out and put their own spin on the concept. Some of my favorites are included below:
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