Tenzij er dus energie toegevoerd wordt vanuit een tot op heden over het hoofd geziene energiebron. Ik heb al eens heel epistel geschreven over hoe dat precies zit:pc1mb schreef:Een isotrope straler heeft - in de transversale wereld - per definitie geen gain.
Antennegain is gedefinieerd als bundeling van het toegevoerd vermogen in een bepaalde richting.
Een antenne die in alle richtingen gelijk straalt, zal z'n 'input' vermogen echter altijd moeten verdelen over 4 pi steradian en kent dus een harde bovengrens in afgegeven veldsterkte. Anders gezegd: een isotrope straler met gain is een perpetuum mobile.
Negatieve gain door (warmte)verliezen is natuurlijk wel mogelijk.
http://peswiki.com/index.php/Article:Fr ... d_Practice
Laat ik het meest intrigrerende deel maar quoten:
Kern van dat betoog is dat het electrisch veld een *dynamische* kracht is. "Iets" stroomt langs/rond de geleiders in onze schakelingen dat vervolgens de ladingsdragers voortstuwt. Zie vooral ook deze MIT demo, waarin een condensator uit elkaar gehaald wordt en waaruit blijkt dat de in een condensator "opgeslagen" energie in ieder geval niet wordt opgeslagen doordat er electronen op de condensator platen blijven hangen:There is an essential difference between the Newtonian analogy we use in electrical engineering (closed circuits) and the actual reality. The analogy of a capacitor in hydraulics (Newtonian analogy) is a piston moving back and forth in a closed cylinder wherein gas is pressurized. And here's the difference: Imagine moving the piston inwards, pressurizing the gas, and put the thing on your workbench. The piston will immediately move back, because of the gas pressure. Now charge a capacitor and put it on your workbench. See the difference? The capacitor will just sit there, keeping it's charge. In other words: our hydraulic analogy is unstable, it 'wants' to release it's energy, while our actual electrical component is stable when 'pressurized'. It will only 'release' it's energy when something external is being done. It has to be disturbed, because the charges in a capacitor actually attract one another, which makes them like to stay where they are. So, when 'discharging' a capacitor, as a matter of fact, these attraction forces have to be overcome. And that does not release energy at all, it costs energy to do that. So, it actually takes the same amount of energy to charge a capacitor as the amount of energy it takes to discharge the capacitor.
It is undoubtedly because of this that Steinmetz wrote, already in the beginning of the twentieth century:
"Unfortunately, to large extent in dealing with dielectric fields the prehistoric conception of the electrostatic charge (electron) on the conductor still exists, and by its use destroys the analogy between the two components of the electric field, the magnetic and the dielectric, and makes the consideration of dielectric fields unnecessarily complicated. There is obviously no more sense in thinking of the capacity current as current which charges the conductor with a quantity of electricity, than there is of speaking of the inductance voltage as charging the conductor with a quantity of magnetism. But the latter conception, together with the notion of a quantity of magnetism, etc., has vanished since Faraday's representation of the magnetic field by lines of force."
So, it may seem that the conservation law holds when considering electrical circuits in their 'prehistoric' analogy, in actual truth this is only the case because the interactions with the environment, the active vacuum, balance one another out. In reality twice the amount of work has been done than seems to having been done!
http://www.youtube.com/watch?v=9ckpQW9sdUg
Afijn, in die andere thread nader toegelicht.
