The motorists here tried to censor me again.
in [UK Drivers]
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From: boltar2003 on 7 Jul 2010 09:24 On Wed, 07 Jul 2010 14:10:53 +0100 Albert T Cone <a.k.kirby(a)durham.ac.uk> wrote: >boltar2003(a)boltar.world wrote: >> On Tue, 06 Jul 2010 23:15:13 +0100 >> Derek Geldard <impex(a)miniac.demon.co.uk> wrote: >>> I'll lend you my copy of "Electronic Processes in Materials" (L V >>> azaroff and JJ brophy) if you like. >> >> Why, don't you need a doorstop anymore? >> >> The beam coming off a cathode in a CRT is electrons (and hence current) >> flowing through a vacuum. See if that book can argue otherwise. > >Point of order - it isn't a vacuum, 'cos it has electrons in it. In that case space isn't a vacuum either because some of it has matter in it. >Also, I reckon you are being a bit disingenuous in bringing thermionic >emission into this. I don't see why. >That said, whilst electrons can't pass through a vacuum, Eh? >electric fields >can and it is quite possible to have a vacuum-filled capacitor - an >example of electrical power being coupled through a vacuum. Well yes. But he wasn't talking about potential , he was talking about actual current. And yes you can have current pass through a vacuum. The link between the earth and the sun is probably the biggest we know of. http://en.wikipedia.org/wiki/Birkeland_current B2003
From: Derek Geldard on 7 Jul 2010 21:10 On Wed, 7 Jul 2010 13:24:30 +0000 (UTC), boltar2003(a)boltar.world wrote: >On Wed, 07 Jul 2010 14:10:53 +0100 >Albert T Cone <a.k.kirby(a)durham.ac.uk> wrote: >>boltar2003(a)boltar.world wrote: >>> On Tue, 06 Jul 2010 23:15:13 +0100 >>> Derek Geldard <impex(a)miniac.demon.co.uk> wrote: >>>> I'll lend you my copy of "Electronic Processes in Materials" (L V >>>> azaroff and JJ brophy) if you like. >>> >>> Why, don't you need a doorstop anymore? >>> >>> The beam coming off a cathode in a CRT is electrons (and hence current) >>> flowing through a vacuum. See if that book can argue otherwise. >> >>Point of order - it isn't a vacuum, 'cos it has electrons in it. > >In that case space isn't a vacuum either because some of it has matter in it. > Read it again. I said absolute vacuum. >>Also, I reckon you are being a bit disingenuous in bringing thermionic >>emission into this. > >I don't see why. > >>That said, whilst electrons can't pass through a vacuum, > >Eh? > >>electric fields >>can and it is quite possible to have a vacuum-filled capacitor - an >>example of electrical power being coupled through a vacuum. > >Well yes. But he wasn't talking about potential , he was talking about >actual current. And yes you can have current pass through a vacuum. The >link between the earth and the sun is probably the biggest we know of. > Please expand on that. >http://en.wikipedia.org/wiki/Birkeland-Eyde_process > >B2003 >
From: Albert T Cone on 8 Jul 2010 03:55 boltar2003(a)boltar.world wrote: > On Wed, 07 Jul 2010 14:10:53 +0100 > Albert T Cone <a.k.kirby(a)durham.ac.uk> wrote: >>> The beam coming off a cathode in a CRT is electrons (and hence current) >>> flowing through a vacuum. See if that book can argue otherwise. >> Point of order - it isn't a vacuum, 'cos it has electrons in it. > > In that case space isn't a vacuum either because some of it has matter in it. Indeed, you ask anybody who works with hard vacuums and they'll tell you that space is a very good partial vacuum. On average, in deep space you get about 1 hydrogen atom per cubic metre, so if you sample a region much smaller than 1 cubic metre you may indeed have a true vacuum, briefly. >> Also, I reckon you are being a bit disingenuous in bringing thermionic >> emission into this. > > I don't see why. Because you are introducing an electron source which isn't present in the more normal forms of conduction which were under discussion. > >> That said, whilst electrons can't pass through a vacuum, > Eh? that is to say that it is no longer a vacuum. >> electric fields >> can and it is quite possible to have a vacuum-filled capacitor - an >> example of electrical power being coupled through a vacuum. > > Well yes. But he wasn't talking about potential , he was talking about > actual current. And from an external perspective thats exactly what you get. > And yes you can have current pass through a vacuum. The > link between the earth and the sun is probably the biggest we know of. You can accelerate charged particles in a field in the absence of other matter, certainly. I won't raise the question of vacuum again. The Jupiter-Io flux tube current (10^8 Amps) is rather higher than the earth magnetosphere currents (~10^6 A), and solar prominences are several orders of magnitude higher than those (~10^12A). If you want serious currents, then you need to look further afield, at the lobes of radio galaxies, the accretion discs of black holes and, according to some, QSOs.
From: boltar2003 on 8 Jul 2010 04:53
On Thu, 08 Jul 2010 02:10:22 +0100 Derek Geldard <impex(a)miniac.demon.co.uk> wrote: >>In that case space isn't a vacuum either because some of it has matter in it. >> > >Read it again. I said absolute vacuum. What difference does it make? The vacuum in a CRT is good enough so that the majority of the electrons are highly unlikely to encounter any atoms on their trip to the screen which means they're not using atoms some sort of transfer mechanism. >>Well yes. But he wasn't talking about potential , he was talking about >>actual current. And yes you can have current pass through a vacuum. The >>link between the earth and the sun is probably the biggest we know of. >> > >Please expand on that. Read the wiki page I posted. B2003 |