Conventional flow has its uses. Just consider that the picture on the crt is produced by opening the flow of current to the cathodes at just the right time and in just the right amount for the light to turn into electricity and jump into the power supply so it can be drained into the wall outlet. It is this kind of magic that keeps us employed.

OK, leaving the good humor of this joke aside for a moment (which I certainly appreciate), this kind of viewpoint, that conventional current says something nonphysical, is exactly the reason why I made my initial comment in this thread. Basically, I don't understand why some people insist on interpreting the conventional current convention in a non-physical way.

Insisting that conventional current is saying that positive charges are going in the direction of the arrow (from + to -) is silly, when you know the device or situation involves electron flow. We all know it's electrons moving and conventional current labels and describes the direction and magnitude of electron flow just as well as the electron flow convention does.

To make an analogy, conventional current is a kind of backwards labeling method similar to labeling public restrooms as "no men allowed" and "no women allowed", or with the male and female stick-figures with a circled X through them, like a no-smoking sign. Is such a thing backwards and awkward and even a little confusing at first? ... yes, but it is no less precise or accurate than labeling the doors as "men" and "women". And, if everyone labeled the rest rooms this way, you would eventually get used to it and have no problems with walking in the wrong door.

So the current arrow in conventional current descriptions is just telling you which way the electrons are not flowing. Is it backwards? ... Sure, but it's backwards because the labeling of the most common charge carrier is also backwards making it less compatible with preexisting language and preexisting standards/conventions in classical mechanics.

So, where is a place we might want classical mechanics and electromagnetics to be compatible? Hmmm, how about when we are dealing with motors and generators? That's a subject introduced about a year after basic circuits in most electrical engineering programs. So, who wants to post the correct version of Maxwell's equations and Newton's equations along with the Lorentz force Law that uses electron flow rather than conventional current flow? Can you even do that without breaking another common sense convention? Does anyone here try to do it that way? Personally, I'd rather use conventional current notation, with full confidence that I'll get my signs correct, and trust me, I'll know which way the electrons are flowing, and won't start wondering if my final answers are saying that protons miraculously started flowing and that I'm now due a Nobel prize in physics.

 

Mixed emotions.

Hey, that was really funny!

Nobody's laughing.

Oh well. At least it served as a bad example.

 

Scientists believe that after the Big Bang there should have been equal quantities of matter and anti-matter. For some yet unknown reason matter won out and most of what we now observe is matter.

Who is to say that we are not all anti-matter!

As tom66 says:

"Pray that there's intelligent life somewhere in outer space 'cause there's bugger all here on planet earth!"

 

I see antimatter all the time. The women (wife, daughters, granddaughters) in my family create it as needed (strangely, intermittently while they're vacuuming) and use it for their nefarious purposes. When they come in contact with my wallet, it disappears with exactly 1 MeV, where MeV stands for millions of elementary VISA receipts. When I ask them where my money went, they just say, "Aw, don't worry, it doesn't matter...".

 

"it ain't matter"

Ha ha... good humor!

 

Conventional flow has its uses. Just consider that the picture on the crt is produced by opening the flow of current to the cathodes at just the right time and in just the right amount for the light to turn into electricity and jump into the power supply so it can be drained into the wall outlet. It is this kind of magic that keeps us employed.

Electron flow 'Conventional or otherwise" in a CRT is mostly irrelevant to the actual transmission of energy because the EM fields that really carry the energy to the phosphor causing it to glow can be detected from quite a distance with the proper equipment.

http://www.lightbluetouchpaper.org/2006/03/09/video-eavesdropping-demo-at-cebit-2006/

http://www.youtube.com/watch?v=mcV6izFG3vQ

http://www.youtube.com/watch?v=HjIhS_JQ80k

 

I'm sure that millions of television viewers will be happy to know that can watch their TV's from quite a distance using only the equipment in your links if their CRT goes bad.

 

I'm tempted to start a new thread since this was seems to have been a bit derailed - but as a complete newbie I'm having a bit of trouble understanding the Conventional versus electron flow section. Questions that come up for me:

1. With the conventional flow notation, the book starts off by seemingly switching the + or - signs and showing the current flowing from the surplus of electrons (labeled +) to the deficiency (labeled -). The flow arrows are therefore correct. This is emphasized by the fact that the caption says "electric charge moves from the positive (surplus) side of the battery to the negative (deficiency) side". But this is contracted a bit later when it says that "we show the motion of charge according to the (technically incorrect) labels of + and -. This way the labels make sense, but the direction of charge flow is incorrect". I'm guessing that this latter sentence is correct, but it would be easier to understand if the caption was changed. My interpretation is that there is no surplus of electrons in the + side under conventional flow. There are two ways that conventional flow could have been adopted: the signs could be reversed, or the charge direction could be reversed. Reversing the signs actually seems like it makes more sense, but it appears that the charge was reversed. It is still a bit mind-boggling to me that one would want to reverse the flow direction and make it inaccurate...

2. The next sentence that throws me is "Many electrical devices tolerate real currents of either direction with no difference in operation. Incandescent lamps (the type utilizing a thin metal filament that glows white-hot with sufficient current), for example, produce light with equal efficiency regardless of current direction." So, maybe I should just read ahead to figure this out - but I thought current only flowed from the negative to the positive? I thought even alternating current worked that way.

3. The section mentions that the diode symbol looks neater when using conventional flow. If the diode symbol was moved down to the bottom line, its direction would fit with the electron flow diagram. Why not do that?

 

At the risk of ducking bullets, I join in seriously...

You seem to have found an error in your book. Electrons carry a negative charge and they are the thing that moves. You can think in those terms or you can think in terms of conventional current by pretending that some kind of mysterious plusatron is in abundance on the positive terminal. It works for me. You just have to be careful not to mix them up.

2) In alternating current, the (power grid) voltage actually reverses every 50th or 60th of a second, depending on where you live. The electrons are still moving toward the lack of electrons, but the alternators keep switching the voltage around so they just dance back and forth. This is necessary because DC will not work in transformers, and all local power is supplied through transformers.

3) The diode symbol is as entrenched as conventional flow. I doubt you will see this rectified (pun) on this planet, ever.

 

I'm tempted to start a new thread since this was seems to have been a bit derailed - but as a complete newbie I'm having a bit of trouble understanding the Conventional versus electron flow section. Questions that come up for me:

1. With the conventional flow notation, the book starts off by seemingly switching the + or - signs and showing the current flowing from the surplus of electrons (labeled +) to the deficiency (labeled -). The flow arrows are therefore correct. This is emphasized by the fact that the caption says "electric charge moves from the positive (surplus) side of the battery to the negative (deficiency) side". But this is contracted a bit later when it says that "we show the motion of charge according to the (technically incorrect) labels of + and -. This way the labels make sense, but the direction of charge flow is incorrect". I'm guessing that this latter sentence is correct, but it would be easier to understand if the caption was changed. My interpretation is that there is no surplus of electrons in the + side under conventional flow. There are two ways that conventional flow could have been adopted: the signs could be reversed, or the charge direction could be reversed. Reversing the signs actually seems like it makes more sense, but it appears that the charge was reversed. It is still a bit mind-boggling to me that one would want to reverse the flow direction and make it inaccurate...

2. The next sentence that throws me is "Many electrical devices tolerate real currents of either direction with no difference in operation. Incandescent lamps (the type utilizing a thin metal filament that glows white-hot with sufficient current), for example, produce light with equal efficiency regardless of current direction." So, maybe I should just read ahead to figure this out - but I thought current only flowed from the negative to the positive? I thought even alternating current worked that way.

3. The section mentions that the diode symbol looks neater when using conventional flow. If the diode symbol was moved down to the bottom line, its direction would fit with the electron flow diagram. Why not do that?

Actually you hit the section of the book that defines the two standards. Like I said, you have to give some acknowledgment to conventional, it was the standard for well over a century. When it was invented the model of the atom didn't exist, no protons, no electrons. They knew something was flowing, but not what. As a model it explained the facts as they knew them. Atoms were thought of as the smallest particles you could have and still have the characteristics of the element, and that was pretty much it. However, a lot of electronics were developed using this theory.

It wasn't until the early 20th century that subatomic particles (which includes electrons) were conceived of.

Here is the section you were talking about:

However, because we tend to associate the word "positive" with "surplus" and "negative" with "deficiency," the standard label for electron charge does seem backward. Because of this, many engineers decided to retain the old concept of electricity with "positive" referring to a surplus of charge, and label charge flow (current) accordingly. This became known as conventional flow notation:

Others chose to designate charge flow according to the actual motion of electrons in a circuit. This form of symbology became known as electron flow notation:

While folks keep saying it doesn't matter, I can name 10 cases where it does. Only electron flow accounts for the physics. Even CRTs use a stream of electrons (and guide them with magnetic fields) to hit the phosphor in a vacuum and make it glow, not an EM field as has been stated. The neck of a CRT is referred to as an electron gun, with reason.

Where it gets confusing is while electrons in wires are the medium we usually think about, it isn't true in liquids and chemical reactions (especially in chemical reactions). There it is ions (many positive) that are the carriers the charge flow, so there are exceptions.

 

This tired argument again? It's really REALLY simple people:

By CONVENTION, current goes from positive to negative. If you think anything else you are violating the CONVENTION.

Conventions are a good thing, least we all first have to make up our own terms, then have to explain what we mean to other people, which would be impossible without some common CONVENTION of definitions we all agree upon.

 

Convention used to say the earth was flat. This was a good thing.

 

While folks keep saying it doesn't matter, I can name 10 cases where it does. Only electron flow accounts for the physics. Even CRTs use a stream of electrons (and guide them with magnetic fields) to hit the phosphor in a vacuum and make it glow, not an EM field as has been stated. The neck of a CRT is referred to as an electron gun, with reason.

I guess we are back to the old saw that electrons are only the charge carriers and the energy required in Cathodoluminescence (CL) is actually transported by a (detectable as RF when the beam is modulated) EM field generated from the second anode voltage. That electrons are an effective means of energy transmission at low frequencies is a given and CL is usually explained with valance bands, holes and electrons instead of kinetic energy.

http://serc.carleton.edu/research_education/geochemsheets/CLTheory.html

 

As I recall the older CRTs (as in older TVs) also came out with some Xray radiation too. The issue was minimized in later models, but it has always been a problem. A cathode ray gun is modified to use in real Xray machines too. As I understand it, it starts with a stream of electrons first though.

It is important to note the electron stream is in a vacuum.

 

As I recall the older CRTs (as in older TVs) also came out with some Xray radiation too. The issue was minimized in later models, but it has always been a problem. A cathode ray gun is modified to use in real Xray machines too. As I understand it, it starts with a stream of electrons first though.

It is important to note the electron stream is in a vacuum.

The transit times of the electrons in the vacuum at typical oscilloscope acceleration voltages (2kV 0.2c) is still a fraction of the speed of energy flow (~ light speed). This makes high speed deflection and dot writing speeds a hard nut to crack without methods to delay the modulation to match the (slower) electrons.

 

Thanks a lot, but I still think the section could be more clear. While the caption describes a "historical understanding", from a newbie perspective conventional flow could be a reversal of the signs or reverse pf the charge flow - and the caption makes it seem like they may be reversing the signs rather than the electrical flow.

Also, Bill, I appreciate the comment about how the charge could be carried by positive ions in liquids and chemical reactions - and if maybe adding that to the section in a brief sentence could increase understanding. It certainly alleviates some of my confusion.

The Wikipedia page, over at Electric_current#Conventions, also mentions that positive flow can happen except with metals:

A flow of positive charges gives the same electric current as a flow of negative charges in the opposite direction. Since current can be the flow of either positive or negative charges, or both, a convention for the direction of current which is independent of the type of charge carriers is needed. Therefore the direction of conventional current is defined to be the direction of the flow of positive charges.
In metals, which make up the wires and other conductors in most electrical circuits...

 

When I was a kid trying to learn electronics, I used Forrest Mims books, which use electron current in all their diagrams. This and other misinformation was a major stumbling block to my learning, and I didn't really "get it" until college, when I learned that everyone uses conventional current, and it's not any more or less wrong than electron current.

Electron current can't explain batteries, fluorescent tubes, electrolytic capacitors, or the Hall effect in semiconductors. Electric current in ice is actually a flow of protons! If you need to worry about the actual charge carriers, then you're doing quantum mechanics, physics or electrochemistry. If you don't have to worry about the individual charge carriers, then you're doing electrical engineering, and you use conventional current to simplify these things out of the equations. Anyone using electron flow to teach electrical engineering needs to include a big disclaimer explaining that they are backwards from everyone else, and learning this way will result in major confusion.

This says it better than I can:

BEN FRANKLIN SHOULD HAVE SAID ELECTRONS ARE POSITIVE? Wrong.

Many authors bemoan the fact that Ben Franklin labeled "resinous electricity" as negative, and "vitreous electricity" as positive. By choosing the polarities this way, Franklin forces us to say that electrons carry a charge of negative electricity. Because of Franklin's decision, we must name the electric currents in metals as flows of NEGATIVE charge rather than positive charge.

Did Franklin make a mistake? Should he have defined the electron to be positive? ABSOLUTELY NOT.

 

Current is charge q multiplied by velocity v.

Charge is a scalar quantity, i.e. it has sign and magnitude, no direction.
Velocity is a vector quantity. It has magnitude and direction.

Electrical current in a common conductor such as a wire is a negative charge (electron) with a negative velocity (flows backwards).

The two negatives cancel out. Electrical current flows in a positive direction from higher to lower electrical potential.

 

Electrical current in a conductor is a negative charge (electron) with a negative velocity (flows backwards).

Nope. It could be electrons, protons, or ions, depending on the conductor.

 

Yep, but in wire, microchips, electron tubes, CRTs, sputtering machines, electronic flame offs, LEDs, transistors, and welders it is electrons that are the charge carriers. You are also off on flourescent tubes, it is the electron flow that creates the ionized gas, another name for plasma. Plasma is used for sputtering machines and electronic flame offs (which particularly depends on electron flow to make sure the material is carried in the proper direction).

When you get into chemical processes it is ions (which are the protons you are naming). Guess what is the majority of our uses for electricity uses? True, it does cover current flow through batteries and other "wet" masses, such as the human body, but in general it is electrons delivered via wires that create the imbalance.

Of course if you want to be more disingenuous you could talk about antimatter, where everything is reversed and we have a completely different set of particles doing the charge carrying.

Electrons can flow freely in a plasma, while the positively charged atoms tend to form fixed masses when they cool. If the element is a metal then electrons can still flow.

Electrons are a form of matter, as are ionized atoms. You can send streams of both, but electrons are much simpler to generate.