which way electrons??

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new guy
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which way electrons??

Post by new guy » Tue Jul 31, 2007 2:44 pm

If current flow is from negative to positive and not the other way around. I was wondering about a car battery. Do the electrons flow from the negative plates inside the batterry over to the positive plates inside the battery and then exit the battery throuhg the positive terminal then through the circuit and return to the negative post. Or do they exit the negative post, go through the circuit and re-enter the positive post and then flow through the battery to the negative plates and back out again. If the second scenario is correct then do the electrons flow from positive plates to the negative plates inside the battery??

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Chris Smith
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Post by Chris Smith » Tue Jul 31, 2007 3:15 pm

It mostly semantics as both show you the way things work.

The technical or scientific understanding is the electrons flow out of the negative post.

English cars and welders use this fact, and there is supposed to be a small gain from using these methods, although the english car battery idea is far fetched.

The welder is supposed to be more efficient and the puddling is more stable.

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haklesup
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Post by haklesup » Tue Jul 31, 2007 3:55 pm

Electrons always exit the negative terminal of a battery. From a physics point of view, "electron current" is from neg to pos. BUT for all calculations in electronics and engineering we use "conventional current flow" which is designated from pos to neg (or higher voltage to lower voltage).

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Post by Robert Reed » Tue Jul 31, 2007 5:15 pm

In the beginning it was thought that electricity flowed from positive to negative. This was disproved by the scientific community years ago ( was it Ben franklin?), but unfortunately, many engineering standards were already in place by then. As Hackle pointed out, the enginneering feild still subscribes to the pos/neg transfer of electricity. Most tech shcools up to Assocites degrees teach electron flow, as not only is it fact, but seems easier to grasp the concept. This has been an ongoing debate between technicians and engineers for ages. If one were to take an egg carton with one missing egg ( visulize the egg as one electron and the empty hole as a positive charge) and start moving each egg from hole to hole, the path of the electrons is travelling in one direction, but viewed from another angle the path of the holes is in the opposite direction. So- are we moving eggs or holes?
Back to your question, its already been stated by Hackle the flow path is negative to positive from the power battery terminals to the load, however within the battery the movement is from the positive terminal to the negative terminal . This holds true with any power source such as line transformer, Etc.

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Post by rshayes » Tue Jul 31, 2007 5:45 pm

Franklin is often credited with making the original mistake. He assumed that charge carriers had positive charge. It really wasn't a mistake since he had no evidence either way. Essentially, he flipped a coin and lost.

The first definitive evidence of the polarity of charge carriers was probably the Edison Effect, which was observed over 100 years later.

Either current convention works, provided you apply it consistently.

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Externet
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Post by Externet » Tue Jul 31, 2007 6:14 pm

Hi.
Electrons flow from negative to positive outside of a battery; and positive to negative inside of a battery.

The conventional schemes are something from the dark electrical days, or because someone decided to come up with such and had enough followers.
Miguel
- Abolish the deciBel ! -

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Chris Smith
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Post by Chris Smith » Tue Jul 31, 2007 7:01 pm

Actually the old ways had no way of checking or finding out what was actually what, so like any 50:50 proposition they went with their best guess and it would be either dead right or dead wrong, but both methods worked just fine for all intents and purposes, so they kept it.

I don’t think they took a poll back then to make a guess, seeing that both explanations were the same, both worked, and neither could be checked.

People just accepted the newly "set" standard and went with it.

Same for most of the early days of science, electronics, light, and all the other branches of science.

How far does a electron actually travel down a conductor?

It will be decades before we actually chart that.

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haklesup
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Post by haklesup » Tue Jul 31, 2007 7:35 pm

The reason for conventional current as it was explained to me was to make the math easier. Theres a lot less subtracting negative numbers from negative numbers and such.

You can flow either way so long as you are consistant but since CAD and simulators all use conventional current, I say: why swim upstream.

You know how confusing a double negative is in language.

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Post by Ed B. » Tue Jul 31, 2007 7:40 pm

All

Please then, explain current flow through the old vacuum tube. The plate had to be positive to attract the electrons from the cathode. Therefore the electrons flowed from negative to positive (outside the battery). How, if possible, did the "HOLES" proceed through the vacuum ?

Ed B.

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Chris Smith
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Post by Chris Smith » Tue Jul 31, 2007 8:24 pm

Electrons and hole pairs refer to solid objects.

Cathode rays are streams of electrons observed in vacuum tubes.


Material with electrical conductivity intermediate between metals and insulators and used in a wide range of electronic devices. Certain crystalline materials, most notably silicon and germanium, have a small number of free electrons that have escaped from the bonds between the atoms. The atoms from which they have escaped possess vacancies, called holes, which are similarly able to move from atom to atom and can be regarded as positive charges. Current can be carried by both electrons (negative carriers) and holes (positive carriers). Such materials are known as intrinsic semiconductors.

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Post by Robert Reed » Tue Jul 31, 2007 8:46 pm

Ed B. wrote:All

Please then, explain current flow through the old vacuum tube. The plate had to be positive to attract the electrons from the cathode. Therefore the electrons flowed from negative to positive (outside the battery). How, if possible, did the "HOLES" proceed through the vacuum ?

Ed B.
Ed
Whats to explain? The electron (current flow) is as you described. Viewed from the other angle, the hole flow is in the opposite direction.

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Post by rshayes » Tue Jul 31, 2007 9:03 pm

Hello Ed,

The Edison Effect was observed in what was essentially a diode vacuum tube. Before this experiment, the carriers of charge could have had either polarity. In a solid, charge can be transferred by charge carriers moving in one direction or by missing charge carriers ("holes") moving in the opposite direction. In a vacuum, there are no stationary charge carriers, and thus no "holes". The direction of charge movement, from a negative cathode to a positive plate, required that the charge carriers have a negative charge.

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Post by Robert Reed » Tue Jul 31, 2007 9:44 pm

RS
In thinking about your last reply, it sounds very feasonable so I may stand corrected. But how would you explain a complete vacuum tube circuit using the convetional current flow theory?

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Chris Smith
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Post by Chris Smith » Tue Jul 31, 2007 9:49 pm

How, if possible, did the "HOLES" proceed through the vacuum ?


They dont.


"Cathode Rays" are streams of electrons in the vacuum tube.

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Post by rshayes » Tue Jul 31, 2007 11:25 pm

Robert Reed,

The vacuum tube disproves the conventional current flow theory. By the time this was done, people had already been assuming that charge carriers were positive for over a hundred years. For most analysis, the results are the same no matter which convention is used.

The use of water flow as an analog for current flow may have had something to do with this. Water flows downhill, from the point of greatest potnetial energy to the point of least potential energy. Electron currrent flow does the opposite. The electrons move from the lowest potential energy to the highest. A world where water flows uphill might be more difficult to explain. The convention could have been changed, but it would also have rippled over into Physics and probably have required several sign changes in Maxwell's Equations, Ampere's Law, and Gauss's Law.

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