Is it possible for electricity to jump a vacuum gap? If so, what is it called when that happens?
Yes. Otherwise those old Fleming tubes wouldn't work...
Arching or conduction depending on the amount of current and suddenness of onset.
It takes more voltage to get it going since air and moisture make better conduction paths. I seem to remember 30Kv/inch for an electrical arc in a vacuum, but I could be way off.
Before transistors, radio and TV sets used vacuum tubes, which are based on electron flow.
In vacuum tubes, the electron current is called thermionic emission and plate current. The current is not visible, but the plates sometimes turn red hot.
With very high electric field gradients in very vacuum, field emission of electrons is possible, with lots of x-rays as the accelerated electrons hit the other side.
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