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## Re: [Amps] "Conventional" current flow and Physics 101

 To: Re: [Amps] "Conventional" current flow and Physics 101 "Jim Garland" <4cx250b@miamioh.edu> Tue, 1 Nov 2016 16:40:33 -0600 mailto:amps@contesting.com>
 ```Ron and Bill and any others interested in this thread, sorry to keep disagreeing with you gentlemen, but I believe your skepticism about "conventional" current is based on a misunderstanding of the concept. It has nothing to do with a "mistake" about the sign of the electron. Let me try to explain, starting with where I think we agree. Yes, electric current as understood by scientists and engineers is a defined quantity, and in that respect it is "imaginary." It is a mathematical abstraction which turns out to be hugely important to understanding the laws of nature and the operation of electronic circuits. In some ways "current" is analogous to "temperature," or "wind," or "pressure," which also are defined abstract quantities. This is what I meant when I said that electric current is a "statistical" quantity. An electric current is only defined in the context of the average flow of large numbers of charge carriers. "Wind" is a similar concept, so let me use that as an example. When a wind blows through a window, we know the wind is made up of a huge number of air molecules. These molecules move at a speed of hundreds of feet per second, and they travel in all directions, colliding and bouncing off each other every micron or so. Even if the air is completely still, the molecules are moving and colliding, and exchanging kinetic energy. This is the thermal motion of the air, and the air temperature is a measure of how frenetic that motion is. If the air is nearly a vacuum, however, with only a few air molecules, then it doesn't make sense to speak of wind, or air temperature, or air pressure, because those quantities have no meaning unless there is a large enough number of molecules to have an averaging effect. It's the same way with electric current. The beam current in a CRT, for example, is only defined in terms of the average behavior of large numbers of electrons. Those electrons travel from the CRT cathode to the phosphor screen, where they are collected and returned to the power supply. The beam current can be measured by an ammeter in the cathode lead, but one can't describe the motion of individual electrons by that current. So yes, individual elections are emitted by the cathode and strike the phosphor screen after a transit time. However, the current flows in the reverse direction, because the current (a) only pertains to the average motion of zillions of elections, and (b) the direction of the current is arbitrarily defined to be the direction of positively charged carriers, even if the actual carriers are negatively charged electrons. It's the same with plate current in a vacuum tube. The current flows inside the tube from plate to cathode, even though the electrons move in the opposite direction. By the way, the technical term for the motion of individual electrons in a vacuum tube, or CRT, is called "ballistic motion," which means that the electrons are moving without colliding with anything during their trajectory. So what's the point of defining a quantity that seems so counterintuitive? Turns out there are very important reasons. First, electric current doesn't depend on the sign of the carriers, and that's a good thing. It would be horribly confusing if we had to keep track of electrons, holes, protons (as in a particle accelerator), ions (as in a battery), solar wind (a mix of all kinds of charged particles), every time we wanted to describe something's electrical properties. There are just as many positive charges in the universe as negative charges (so far as we know), so there's no reason to give preference to one polarity over the other. Intuitively, the positive sign convention makes good sense. An electric field from a positively charged particle radiates outwards from the particle, which seems more natural than having electric field lines converge in on the particle from infinity. The forces on moving charges created by a magnetic field can be described by a so-called "right hand rule," which is easy to remember since most people are right-handed. Similarly the direction of the magnetic field lines created by an electric current is described by another right-hand-rule. And for ham operators, it's very intuitive to think of current as flowing out of the positive terminal of a battery or B+ supply and returning to ground and eventually back into the negative terminal. Kirchhoff's law (which states that the steady state current flowing into a node (junction) has to leave the node at the same rate) is at the heart of all circuit theory. That law depends on current flow being independent of the sign of the underlying charge carriers. There are many other reasons why "conventional" current is an essential concept. Part of the confusion about current flow versus charge motion is actually the fault of the US Army. Back in WWII days, army training manuals often confused the two concepts, ultimately misleading generations of electronic techs. Some of the drawings in those days showed current flowing out of the negative terminal of a battery through a resistor and into the positive terminal. That's true for electrons, but not for the electric current! 73, Jim W8ZR > -----Original Message----- > From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Ron Youvan > Sent: Friday, October 28, 2016 04:46 PM > To: amps > Subject: Re: [Amps] "Conventional" current flow > > Jim W8ZR Garland wrote in part: > > >> Concur with Bill W6WRT re "positive vs negative" convention in > >> describing > > current. The > >> convention we use now is left over from at least a hundred years ago > >> when > > a scientist > >> guessed wrong about the polarity of the electron. To me, thinking in > > terms of the direction > >> of electron movement is far more clear. > >> -Gene WB8WKU > > > Sorry to disagree with you and Bill, Gene, but the standard convention > > for electric current makes a lot of sense, and it's not just that > > somebody guessed wrong a century ago about the polarity of electrons. > > The important concept is that electric current is a statistical > > concept. Electric current is sometimes carried by positive charges, > > sometimes by negative charges, but the sign of the charge carrier is > > an entirely separate issue from the direction of current flow. In a > > vacuum tube, plate current flows into the plate and out of the > > cathode, even though the motion of the electrons in the tube envelope > > is in the reverse direction. Similarly, current flows into the > > collector of an NPN transistor and out the emitter (hence the words > > collector and emitter), even though transistor current may be carried > > by holes. Similarly, current flows out the positive terminal of a > > battery and returns into the negative terminal, no matter whether the > > charge of the ions in the battery are positively or negative. It would > > be a nightmare to keep track of current flow, if the direction of flow > > depended on the sign of the underlying charge carriers. You might > > have situations where current flows out of a B+ supply to the plate of > > a tube, and then is annihilated by current flowing in the opposite direction from within the > tube, coming from the cathode. > > Bull! Conventional current flow was a wrong guess. > I'm sorry I must say ... > Please explain to us how the CURRENT flows up the ultor lead to the side of the bell of > the cathode ray tube, runs in and around the aquadag inside the bell and at the right place > jumps off and strikes that precise spot on the screen (that is based on the magnet field that > the current is yet to pass though) then is shoots through that varying magnet field (when it is > at the exactly correct magnitude) at high velocity at a tiny hole in the end of the electron > gun, (which under no circumstance fails to go through) and lands ONLY on the only hot > thing at the bottom of the gun. > Yea sure! > > The flow of holes through conducting materials is the RESULT of the motion of > ELECTRONS. To say other wise makes me say BULL. > > Only some (older) larger universities and a few manufacturing companies (GE and a few > others) hang on to the obsolete conventional current flow that should be forgotten by > everyone. Why? Because electrons are what IS MOVING. The flow of electron is > electricity. > (and lighting) > -- > Ron KA4INM - Youvan's corollary: > Every action results in unwanted side effects. > _______________________________________________ > Amps mailing list > Amps@contesting.com > http://lists.contesting.com/mailman/listinfo/amps _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps ```
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