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Could the absence of a medium also be considered an insulator? The description of Thermionic emission on Wikipedia (http://en.m.wikipedia.org/wiki/Thermionic_em

by sjtrny 12y ago

Could the absence of a medium also be considered an insulator? The description of Thermionic emission on Wikipedia (http://en.m.wikipedia.org/wiki/Thermionic_emission http://en.m.wikipedia.org/wiki/Thermionic_emission) seems general enough that things like rubber and vacuums are both insulators in some sense.

privong 12y ago
Thermionic emission just refers to releasing electrons from the surface of a material by heating up that material (which is what happens in a vacuum tube). But it doesn't specifically deal with what happens to the electrons after they leave the surface of the material. I am not sure what part of the wikipedia article you are referring to – the word "insulator" isn't used anywhere in the article.
tjradcliffe 12y ago
"Insulator" usually means "made of insulating material", and a vacuum is not made of material. :-) Language is ambiguous, so it's important when asking questions like this to be really clear about what you mean by terms. In particular: "insulator" is a term of convenience that groups together materials of sufficiently low conductivity under fairly normal conditions. What constitutes "sufficiently low" and "fairly normal" are both highly context dependent. Heat anything up enough and it'll become a conductor (it'll also become a plasma). If you use a term like "insulator" without keeping all this in mind it'll produce some pretty weird results. So you can answer this question all kinds of ways. In normal high-voltage parlance, vacuums are considered insulators. But unlike insulating materials, which are full of electrons that can't move, vacuums are insulators purely because they don't contain any electrons. If you inject electrons, the vacuum becomes a conductor... or at least the electrons do. After all, a vacuum is an absence of matter, and where there is an electron there is matter, so where there is an electron there is not a vacuum...
kazinator 12y ago
Sure. Vacuum is an insulator until you exceed its breakdown voltage, just like other insulators. Electricity will go through a vacuum just like it will go through a polyester film or whatever.

by sjtrny 12y ago

privong 12y ago

Thermionic emission just refers to releasing electrons from the surface of a material by heating up that material (which is what happens in a vacuum tube). But it doesn't specifically deal with what happens to the electrons after they leave the surface of the material. I am not sure what part of the wikipedia article you are referring to – the word "insulator" isn't used anywhere in the article.

tjradcliffe 12y ago

"Insulator" usually means "made of insulating material", and a vacuum is not made of material. :-) Language is ambiguous, so it's important when asking questions like this to be really clear about what you mean by terms. In particular: "insulator" is a term of convenience that groups together materials of sufficiently low conductivity under fairly normal conditions. What constitutes "sufficiently low" and "fairly normal" are both highly context dependent. Heat anything up enough and it'll become a conductor (it'll also become a plasma). If you use a term like "insulator" without keeping all this in mind it'll produce some pretty weird results. So you can answer this question all kinds of ways. In normal high-voltage parlance, vacuums are considered insulators. But unlike insulating materials, which are full of electrons that can't move, vacuums are insulators purely because they don't contain any electrons. If you inject electrons, the vacuum becomes a conductor... or at least the electrons do. After all, a vacuum is an absence of matter, and where there is an electron there is matter, so where there is an electron there is not a vacuum...

kazinator 12y ago

Sure. Vacuum is an insulator until you exceed its breakdown voltage, just like other insulators. Electricity will go through a vacuum just like it will go through a polyester film or whatever.