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Right. I see now that I was unclear in that second part - I should have written something like "just because EM waves can propagate in vacuum does not mean you
by twtw 8y ago
Right. I see now that I was unclear in that second part - I should have written something like "just because EM waves can propagate in vacuum does not mean you can induce a current density in vacuum." Of course EM waves can induce current density in antennas and other structures.
> Obviously you can't induce a current in vacuum ...
Yes. I wrote that second part because 'mmmBacon seemed to be arguing that one could induce a current in vacuum; that because vacuum has a characteristic impedance, it isn't an insulator (i.e. can support current because it has characteristic impedance).
- analognoise 8y agoAh, gotcha, appreciate the clarification.
- mmmBacon 8y ago@twtw was not arguing that one can induce a current in the vacuum. However, I did say that a surface can arc in vacuum. This is because a surface can emit charges either thermally or in presence of a large electric field. This is correct and didstinct from current induction in media. Please note this phenomenon should not be confused with arc discharge in gas. See: https://en.m.wikipedia.org/wiki/Vacuum_arc https://en.m.wikipedia.org/wiki/Vacuum_arc
- twtw 8y agoRight, but that effect is pretty much unrelated to the characteristic impedance of free space and doesn't mean that vacuum is not an insulator.
- mmmBacon 8y agoI’m sorry but I fundamentally disagree. GP said vacuum is a perfect insulator. Comment was in response to that demonstrating that it is not.