Actually serious, and for the record, a fluid analogy is quite accurate for macroscopic eletrical current. It just has to be envisioned within a roughly two-dimensional universe.
>-----Original Message----- >From: [EMAIL PROTECTED] >[mailto:[EMAIL PROTECTED] On Behalf Of Bagotronix >Tech Support >Sent: Wednesday, August 03, 2005 2:02 PM >To: Protel EDA Discussion List >Subject: Re: [PEDA] Vias. > >[EMAIL PROTECTED] wrote: > > And you both forgot that like water in a pipe, electrons >will migrate to > the side of the via in which the flow is >occuring, further reducing the > effective "trace width" of the via... > >I can't tell if aj is joking or serious... > >If we are going to use analogies to describe current flow, >let's at least use correct ones. > >Current flow is the movement of electric charge through a >medium. The medium can be either conductive or >non-conductive. If the medium is conductive, then you have >"conduction current", as in current flowing through a wire. >If the medium is non-conductive, you have "displacement >current", as in time-varying current flowing through the >dielectric of a capacitor. > >Electric charge consists of positive or negative charges. At >the atomic level, a positive charge is an atom that is missing >one or more electrons from it's electron orbitals. The >negative charge is a lone electron that has broken away from >the orbital it was in, and is free to travel. Where does it >go? It goes to the next electron-deficient atom it >encounters. It stays for a while, then hops to the next atom. > This process (electron >drift) does not happen at the speed of light, as so many >believe. What does happen is that the electric field travels >through the medium at nearly the speed of light (or some >significant fraction thereof). The actual electrons only >travel a few meters per second. > >Here is the analogy that works: you remember that novelty >item with 5 steel balls suspended in a row by threads? You >pull back one of the steel balls, let it go, and it swings >back and hits the ball next to it. The ball on the other end >of the row swings out and then swings back, while the >3 inner balls stay stationary. The silly thing keeps doing >that "klak-klak" thing for a long time, until air resistance >eventually robs it of the kinetic energy. In this analogy, >the 2 end balls are electrons, the three middle balls are the >conductor, and the kinetic energy is the electric field. Even >though the end balls (electrons) are moving at only a some >fraction of a meter per second, the speed at which the kinetic >energy (electric field) is conducted through the middle balls >(conductor) is much faster than that. > >So, the electrons will not pile up on a particular region of a >via. What you may be thinking of is "skin effect". That >happens when the electric field of a flowing current cannot >penetrate equally through the depth of a conductor, and flows >mostly on the surface of the conductor. This effect becomes >worse as you go higher in frequency. It results in a >reduction of the effective cross-sectional area of a >conductor. If you want to think of that as electron migration >to the surface of the conductor, that is a valid way to think >of it. Maybe that's what you had in mind. Skin effect does >not occur at DC, and is negligible at low frequencies in most >cases. It does become a concern in high-power switching power >supplies and high-tension AC power transmission lines. > >One last item: which way does current really flow? > >Answer: it flows from where there are negative charges >(electrons) to where there are positive charges (atoms missing >an electron). Therefore current does not really flow from + >to -, as we commonly analyze our circuits. Current actually >flows from - to +. So why does our stuff work? > Because unless you are working with the actual physics of >semiconductors and materials, it doesn't really matter which >way the current flows, as long as you choose one direction and >stick with it. What most of us EE's (myself included) use is >called "convential flow", which is + to -, but is incorrect >theoretically. Some EE's use "electron flow", which is - to >+, and is correct theoretically. > >Put that in your academic pipe and smoke it ;-) > >Best regards, >Ivan Baggett >Bagotronix Inc. >website: www.bagotronix.com > > >[EMAIL PROTECTED] wrote: >> And you both forgot that like water in a pipe, electrons >will migrate >> to the side of the via in which the flow is occuring, >further reducing >> the effective "trace width" of the via... >> >> aj > > >____________________________________________________________ >You are subscribed to the PEDA discussion forum > >To Post messages: >mailto:[email protected] > >Unsubscribe and Other Options: >http://techservinc.com/mailman/listinfo/peda_techservinc.com > >Browse or Search Old Archives (2001-2004): >http://www.mail-archive.com/[email protected] > >Browse or Search Current Archives (2004-Current): >http://www.mail-archive.com/[email protected] > > This e-mail transmission and its attachments may contain information from Avtron Manufacturing, Inc. that is proprietary, privileged and/or confidential and is intended exclusively for the person(s) to whom it is addressed. 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