Author Topic: Flow of Electrons in a DC Circuit  (Read 22925 times)

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Offline OpenCircuitTopic starter

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Flow of Electrons in a DC Circuit
« on: March 23, 2017, 05:34:56 am »
OK, I was reviewing diodes (Elementary level here  :-// ) and I am lost as to what direction electrons actually flow in a DC circuit. Checked out a youtube video and the first video that I decide to watch says + to -. Read the first ten comments and the commentators were ripping the guy apart for showing the electrons flowing in the wrong direction.

Another issue that brought this matter up for review was diodes where I thought they described flow in the wrong direction. My question was how can you push electrons through the diode backwards if they do not flow that direction. Can you just flip the diode around and then they will simply flow in the other direction? Seems silly, but I am no EE.

Hope this is not a point of theoretical contention in the field of EE for a thread of war, but I simply do not know after all of this. I sure thought this matter was EE 101 and already solved.  Thanks for any help.
 

Offline Phoenix

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Re: Flow of Electrons in a DC Circuit
« Reply #1 on: March 23, 2017, 06:10:43 am »
Conventional current flow is actually backwards to electron flow. An electron itself is negatively charged. E.g. in a battery there is an excess of electrons at the negative terminal and a shortage at the positive terminal. The electrons are attracted from the negative terminal - through the circuit - and to the positive terminal. However, "conventional current" (defined before electron movement was really understood) is theoretically the flow of a positively charged particle from the positive terminal to the negative terminal.

The arrow pattern of a diode symbol is defined by conventional current flow. The electrons indeed flow through the diode against the arrow.

On a further point - current is not always by electrons; it is the movement of any charged particle. Consider current flowing through salty water - it's the movement of the positively charged Na+ ions and negatively charged Cl- ions that are causing the current to flow.

The definition/convention we settled on for positive current is unfortunately backwards to electron flow.
 
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Offline basinstreetdesign

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Re: Flow of Electrons in a DC Circuit
« Reply #2 on: March 23, 2017, 06:16:42 am »
Electrons do not flow in the usual sense that you may think as traveling from point A to point B at a very rapid rate through a wire.  Instead they tend to drift in a cloud due to applied voltage difference.  But be that as it may (and many a long discussion has been prosecuted about it) they travel from a more negative potential towards a more positive potential.

This is seen most clearly in tube circuits where a hot cathode in a vacuum tube, at a more negatively charged potential, causes electrons to boil off into space and then to be attracted towards a positively charged plate.  The electron current must then find its way through the rest of the circuit back to the cathode somehow.  Thus, electron current flow travels from negative to positive.  However, many people decided that it would make the math seem more intuitive if a convention were defined where positive current flow were defined the other way around, from positive potential to negative potential.

So, today we usually define positive conventional current flow from a more positive potential to a more negative potential while at the same time electron current flow is still from a more negative potential towards a more positive potential.
I hope that's clear

Just to underline the true duality of positive and negative current, semiconductors are thought to pass both negative and positive "charge carriers".  While the negative charge carriers are still electrons, the positive charge carriers are the holes left behind when an electron vacates a position in the crystal lattice.  So positive currents in semis are currents of holes and they have all of the same characteristics of electrons except they travel the other way.
« Last Edit: March 23, 2017, 06:24:52 am by basinstreetdesign »
STAND BACK!  I'm going to try SCIENCE!
 
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Offline OpenCircuitTopic starter

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Re: Flow of Electrons in a DC Circuit
« Reply #3 on: March 23, 2017, 06:45:52 am »
Which is correct:
?

Nothing is simple it seems.  :popcorn: Thanks for the excellent responses by the way.
« Last Edit: March 23, 2017, 06:52:01 am by OpenCircuit »
 

Offline rstofer

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Re: Flow of Electrons in a DC Circuit
« Reply #4 on: March 23, 2017, 07:04:26 am »
Which is correct:
?

Nothing is simple it seems.  :popcorn: Thanks for the excellent responses by the way.

'A' is correct...

Keep it simple, don't think about electron flow at all.  Just think about current flow and realize that it goes the way the arrow is pointing.  This also applies to transistors.  For an NPN transistor, collector and base current all flow out the emitter.  And the arrow is pointing out!

I realize that this is simplistic but you can go a long way without getting into electron flow.
 
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Offline james_s

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Re: Flow of Electrons in a DC Circuit
« Reply #5 on: March 23, 2017, 07:00:13 pm »
Yeah about the only time you have to worry about electron flow is working with vacuum tubes. For solid  state stuff you can just use conventional flow, pretend electrons flow from positive to negative and don't worry about what is actually going on inside the wires. You can't see the electrons anyway.
 
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Offline Ratch

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Re: Flow of Electrons in a DC Circuit
« Reply #6 on: March 24, 2017, 02:07:48 am »
OK, I was reviewing diodes (Elementary level here  :-// ) and I am lost as to what direction electrons actually flow in a DC circuit. Checked out a youtube video and the first video that I decide to watch says + to -. Read the first ten comments and the commentators were ripping the guy apart for showing the electrons flowing in the wrong direction.

Another issue that brought this matter up for review was diodes where I thought they described flow in the wrong direction. My question was how can you push electrons through the diode backwards if they do not flow that direction. Can you just flip the diode around and then they will simply flow in the other direction? Seems silly, but I am no EE.

Hope this is not a point of theoretical contention in the field of EE for a thread of war, but I simply do not know after all of this. I sure thought this matter was EE 101 and already solved.  Thanks for any help.

I have seen a lot of folks get wrapped around the axle by the "conventional flow" and "electron flow" methods.  I hope I can clarify your understanding.

First of all, you and everyone else should not use the technical slang term "current flow".  Current already means charge flow, so that slang term really means "charge flow flow", which is redundant and ridiculous.  You should instead say current exists or current is present, and be syntactically correct.  Even when everyone knows what you mean, slang obfuscates a meaningful description.  You are a student, not a poet. 

Realize that there are just as many positive charges in the universe as negative charges.  Blaming Ben Franklin, switching the  names of the charges, or redefining the direction they move in an electric field is not going to help your confusion.

Although it is not usually not emphasized, the conventional flow method is a mathematical method or  procedure which dictates that positive charges will flow from the positive terminal of the voltage source through a conduction path, and into the negative terminal.  It makes no distinction about the polarity of the charge carrier.

You will get yourself into big trouble and confusion if you approach a problem by first asking, "Are the charge carriers positive or negative"?  And then start to write Kirchoff's equations based on the answer.  The bullet proof method is to first assume that the unknown currents are composed of positive charges.  Then, if you need to really know the true direction of the charge carriers, keep the same direction if the carriers are positive, like holes are, and reverse the direction if they are negative, like electrons are.  Works every time.

By the way, you have probably observed that semiconductor manufacturers have adopted the mathematical convention to mark their devices.  So have manufacturers of ammeters.  So when you put a positive voltage on the positive terminal of an ammeter, it is going to deflect the needle to the right indicating a forward direction.  But since you know that electrons are negative charge carriers, you can deduce that the physical direction of the electrons are in the opposite direction.  Same with a diode.  A positive voltage on the arrow will cause a current to exist.  Any ammeter will show that.  If it is a junction diode, the holes are going to flow in the direction of the arrow, and the electrons are going to flow in the opposite direction.

That is about it.  Just follow the above procedure methodically.  Ask if you have any questions.

Ratch
« Last Edit: March 24, 2017, 02:13:59 am by Ratch »
Hopelessly Pedantic
 
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Offline Ratch

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Re: Flow of Electrons in a DC Circuit
« Reply #7 on: March 24, 2017, 03:02:05 am »
Current is defined as the "equivalent" flow of positive charge, and electron carries negative charge.
Therefore, for a load, current flows from positive input to negative input, and for a source, current flows from negative output to positive input.
Similarly, for a load, electrons flow from negative input to positive input, and for a source, electrons flow from positive output to negative output.

The reason for me to say "equivalent" when mentioning flow of positive charge is because in a dry circuit (no electrolyte or similar things involved), the only carrier in conductor are electrons (once again, not absolutely true, for instance, in semiconductors there are charged ions as carriers, but we first talk about simple copper wires), so the movement of actual positive carriers doesn't exist, therefore we define the opposite of electron movement as positive charge movement.

First of all, as I explained in the post above, it is wrong to say that current flows.  Charge flows, but siince  current is the flow of charge, it does not need to be said that it flows twice.

The charge transport method between metal wires and semiconductors is completely different.  What is a charged ion?  Are not all ions charged?  Otherwise they would not be ions, right?  Anyway, ions in a semiconductor are fixed and therefore immovable, no current is present from ions.

What is an "actual positive carrier"?  Holes do not exist is metal conductors like wire.  They would be instantly annihilated by the sea of electrons in the metal.  Only in in semiconductors to holes exist.  Your response does not appear to be very coherent.

Ratch
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Offline Ratch

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Re: Flow of Electrons in a DC Circuit
« Reply #8 on: March 24, 2017, 03:36:21 am »
First of all, as I explained in the post above, it is wrong to say that current flows.  Charge flows, but siince  current is the flow of charge, it does not need to be said that it flows twice.
The charge transport method between metal wires and semiconductors is completely different.  What is a charged ion?  Are not all ions charged?  Otherwise they would not be ions, right?

Fair enough.
-pedantic -Wextra -Werror

Anyway, ions in a semiconductor are fixed and therefore immovable, no current is present from ions.

Once again, analogy. Holes never move, but the transport mechanism makes it look like holes are moving. Therefore sometimes we say P/N carriers move, but in reality only electrons physically moves.

What is an "actual positive carrier"?  Holes do not exist is metal conductors like wire.  They would be instantly annihilated by the sea of electrons in the metal.  Only in in semiconductors to holes exist.  Your response does not appear to be very coherent.

That's why I said we define something as "it" because "it" doesn't actually exist. It is just convenient to say there is a positive "charge" that moves, which in reality, is the negative charge moving in the opposite direction.

I am glad you agree that I am pedantic.  I cannot help it, so I give everyone warning with my tag line. 

Now, I understand your confusion with holes and electrons.  Holes do have an effective mass and a mobility factor.  They are more than just an absence electrons.  It is convenient to think of them in that simplistic way, but the quantum mechanics of semiconductors gives them a mass and mobility that is different than electrons, and considers them as just another particle. So, holes do exist physically in semiconductors.

Ratch
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Offline Ratch

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Re: Flow of Electrons in a DC Circuit
« Reply #9 on: March 24, 2017, 04:02:03 am »
Once again, analogy. Holes never move, but the transport mechanism makes it look like holes are moving. Therefore sometimes we say P/N carriers move, but in reality only electrons physically moves.

Holes do have an effective mass and a mobility factor.  They are more than just an absence electrons.  It is convenient to think of them in that simplistic way, but the quantum mechanics of semiconductors gives them a mass and mobility that is different than electrons, and considers them as just another particle. So, holes do exist physically in semiconductors.

They exist, and do have effective mobility, but the dopant atoms, mostly boron in silicon, don't move except for thermal diffusion, which happens over an extremely long period of time in normal operating temperature.

The dopant atoms are fixed and the holes they create do move.  Both holes and electrons move and  constitute the charge carriers in a junction transistor.  Because a junction transistor has two carriers (holes and electrons), it is called a bipolar device.  FETs and vacuum tubes are monopolar devices.

Ratch
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Offline Brumby

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Re: Flow of Electrons in a DC Circuit
« Reply #10 on: March 24, 2017, 05:26:55 am »

I am glad you agree that I am pedantic.  I cannot help it, so I give everyone warning with my tag line. 


I've noticed - but might I suggest easing back on this when it comes to the Beginners section.

You don't need to understand the nature of charge carriers to build a circuit, have a lifetime hobby in electronics - or even for a career in EE.

Very often we have people who have no idea on what is going on - and the conventional phrases are useful in building a functionally useful understanding.  Yes, they may be absolutely horrendous in regards to complete accuracy, but they are common terms that are frequently used, because the key concept is being communicated.  This is how I got the feel of how things worked and I was able to create success on the circuit in front of me.  Proper understanding followed later

Once they are comfortable with the basics and they are seeking to expand their understanding, then take things up a level - but at the moment, it is likely to confuse the hell out of a beginner, when it just is not necessary.
« Last Edit: March 24, 2017, 05:31:16 am by Brumby »
 
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Offline Ratch

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Re: Flow of Electrons in a DC Circuit
« Reply #11 on: March 24, 2017, 03:02:07 pm »
The dopant atoms are fixed and the holes they create do move.  Both holes and electrons move and  constitute the charge carriers in a junction transistor.  Because a junction transistor has two carriers (holes and electrons), it is called a bipolar device.  FETs and vacuum tubes are monopolar devices.

It's "unipolar", actually, being pedantic. Also, by saying "junction transistors", I interpret that as JFETs and BJTs, which are completely different things. The former is unipolar (unless you positively bias the gate, but the D-S channel is still unipolar), and the latter is bipolar.

I looked up the definition of unipolar and monopolar and could not differentiate between the two meanings.  They both mean the same thing. 

You are right, I should have said bipolar junction transistor (BJT) to avoid confusion with JFETs.

Ratch
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Offline Ratch

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Re: Flow of Electrons in a DC Circuit
« Reply #12 on: March 24, 2017, 03:15:25 pm »

I am glad you agree that I am pedantic.  I cannot help it, so I give everyone warning with my tag line. 


I've noticed - but might I suggest easing back on this when it comes to the Beginners section.

You don't need to understand the nature of charge carriers to build a circuit, have a lifetime hobby in electronics - or even for a career in EE.

Very often we have people who have no idea on what is going on - and the conventional phrases are useful in building a functionally useful understanding.  Yes, they may be absolutely horrendous in regards to complete accuracy, but they are common terms that are frequently used, because the key concept is being communicated.  This is how I got the feel of how things worked and I was able to create success on the circuit in front of me.  Proper understanding followed later

Once they are comfortable with the basics and they are seeking to expand their understanding, then take things up a level - but at the moment, it is likely to confuse the hell out of a beginner, when it just is not necessary.

I have heard that argument before.  I believe that learning the correct terminology, definitions, and the correct way things work at the beginning helps eliminate the need to "relearn" the correct knowledge later.  Observe the multitude of folks who say and think that current flows.  Furthermore, learning the correct things at the beginning is not that much harder.  I observed that most problems occur because the student does not have a good background of physics.  As you undoubtedly know, physics and math are the foundation sciences of electrical knowledge.

Ratch
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Offline retrolefty

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Re: Flow of Electrons in a DC Circuit
« Reply #13 on: March 24, 2017, 03:29:46 pm »

 I was taught in the military, 1966,  that current (or charge flow if that floats your boat) flowed from negative to positive and that the EE world got it wrong and to ignore their arrows pointing in the wrong direction. Usual push-backs by many is what about 'hole flow'. Well all I know is that copper wires connect all three terminals of most transistors (dual gate FETs use to exist?) are copper based using just electrons movement from neg to pos, case closed.

 :box:
 

Offline james_s

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Re: Flow of Electrons in a DC Circuit
« Reply #14 on: March 24, 2017, 03:33:36 pm »
But why does it matter that it's technically wrong? EE pretends that flow is from positive to negative, that's how all the symbols are drawn, it's called "conventional flow" because the convention is to assume the flow in that direction. From a circuit design perspective it doesn't matter which direction it is actually flowing. EEs know that conventional flow is technically incorrect, but that makes no difference in terms of actually designing a circuit. I don't have to care what is going on inside a transistor to know how to apply one.
 

Online CatalinaWOW

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Re: Flow of Electrons in a DC Circuit
« Reply #15 on: March 24, 2017, 03:52:25 pm »
Which is correct:
?

Nothing is simple it seems.  :popcorn: Thanks for the excellent responses by the way.

As engineers and technicians a more practical response is appropriate.  In one of the two pictures the load will respond.  If it is a resistor it will get hot.  If it is a coil a magnetic field will be generated.  If it is a bulb it will light.  Forget the physicists and their arguments about current flow.  When the plus on the battery is connected on the triangle end of the diode good stuff happens.  When the plus on the battery is connected to the line end of the diode nothing much happens.  Similar reasoning can be applied to transistors and other similar devices.  The symbols we have chosen for our parts may not be pedantically right (from some point of view), but they are the ones that are extremely widely used.  If you stick with them you will understand published circuits, and others will understand your written communications.  Which most people think is a good thing.

When you graduate to AC circuits you won't have to change this understanding much.  And when you are in university level courses on solid state physics you will have sufficient understanding to use either convention without worrying about it too much.
 

Offline Ratch

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Re: Flow of Electrons in a DC Circuit
« Reply #16 on: March 24, 2017, 04:00:52 pm »

 I was taught in the military, 1966,  that current (or charge flow if that floats your boat) flowed from negative to positive and that the EE world got it wrong and to ignore their arrows pointing in the wrong direction. Usual push-backs by many is what about 'hole flow'. Well all I know is that copper wires connect all three terminals of most transistors (dual gate FETs use to exist?) are copper based using just electrons movement from neg to pos, case closed.

 :box:

What the military taught you is correct provided the charge carriers are negative.  That is true in metal wires, but not for positive charge carriers, which exist in P-type semiconductors or certain electrochemical reactions.  The electrical manufacturers did not get it wrong when they deliberately marked their semiconductors and ammeters according to the mathematical designated flow, and allowed the user to easily figure out the real physical direction only if necessary.  The connecting of semiconductor terminals with metallic wires is irrelevant.  No moving positive charges exist is metaqllic wires.  All anyone has to do is not ask "What polarity is the charge carrier?" at the beginning of the problem.

Ratch
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Offline Ratch

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Re: Flow of Electrons in a DC Circuit
« Reply #17 on: March 24, 2017, 04:09:52 pm »
blueskull,

You have proved that "unipolar" is in wide use when describing a transistor whose current consists of a single charge carrier.  You have not proved that "monopolar" is wrong when used in place of uniipolar.  Both those words mean the same thing regardless of the favored usage.

Ratch
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Offline Brumby

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Re: Flow of Electrons in a DC Circuit
« Reply #18 on: March 24, 2017, 04:13:34 pm »
I have heard that argument before.
and clearly dismiss it out of hand.

Quote
I believe that learning the correct terminology, definitions, and the correct way things work at the beginning helps eliminate the need to "relearn" the correct knowledge later.
You see, there is the problem.  All the terminology, definitions and descriptions of the ways things work in a functional sense - and which are universally used across the board in almost every corner of electronics that don't necessitate an understanding of quantum physics (or valves) - use these very terms.

By imposing pedanticism, you are going to confuse the crap out of anyone just getting started - because you say one thing and they encounter the other in 99% of what they read.

Quote
Observe the multitude of folks who say and think that current flows.
Being pedantic ... if current doesn't flow, then you are just talking about charge.  N'est-ce pas?

Quote
Furthermore, learning the correct things at the beginning is not that much harder.
I can just see you now training someone for the high jump.  You are going to go into all the diagrams, muscle dynamics, vectors, CofG and all the maths that goes with it with some poor mug who hasn't even gone over the bar once.  Really motivational - not.

Quote
I observed that most problems occur because the student does not have a good background of physics.
You don't need it to make an LED flash or even build a power supply.

Quote
As you undoubtedly know, physics and math are the foundation sciences of electrical knowledge.
Indeed.  But why bury some poor soul with all this crap WHEN THEY MAY NOT NEED IT for the level of involvement that they choose to enjoy.

If they develop an interest that requires further knowledge, then they can learn at that point.


Let me be blunt.  By being pedantic in the Beginners section, you are doing more harm than good.  IMHO


You can make a perfectly good kite without knowing any aerodynamic terms.
« Last Edit: March 24, 2017, 04:15:27 pm by Brumby »
 
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Offline Ratch

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Re: Flow of Electrons in a DC Circuit
« Reply #19 on: March 24, 2017, 04:33:04 pm »
Which is correct:
?

Nothing is simple it seems.  :popcorn: Thanks for the excellent responses by the way.

As engineers and technicians a more practical response is appropriate.  In one of the two pictures the load will respond.  If it is a resistor it will get hot.  If it is a coil a magnetic field will be generated.  If it is a bulb it will light.  Forget the physicists and their arguments about current flow.  When the plus on the battery is connected on the triangle end of the diode good stuff happens.  When the plus on the battery is connected to the line end of the diode nothing much happens.  Similar reasoning can be applied to transistors and other similar devices.  The symbols we have chosen for our parts may not be pedantically right (from some point of view), but they are the ones that are extremely widely used.  If you stick with them you will understand published circuits, and others will understand your written communications.  Which most people think is a good thing.

When you graduate to AC circuits you won't have to change this understanding much.  And when you are in university level courses on solid state physics you will have sufficient understanding to use either convention without worrying about it too much.

I believe that there is no conflict between the direction of charge flow, and that everything agrees with established physics laws and principles.  Problems occur when folks do not understand the definitions clearly, and therefore apply them wrong.  The basic thing to remember is that conventional current is a mathematical concept, not a physical concept.  Current direction should be determined, if necessary, after the mathematical value is obtained.

Now take the right circuit above.  The diode will allow a mathematical current to exist in a counterclockwise direction, because the diode arrow will positive in relation to its bar.  Since the electrons are negative charge carriers, the true physical current will be in a clockwise direction.  Most of the time the physical current direction will not matter.

Ratch
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Offline james_s

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Re: Flow of Electrons in a DC Circuit
« Reply #20 on: March 24, 2017, 04:56:13 pm »
The poor guy who started this thread is probably more confused now than he was to begin with.
 
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Offline Ratch

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Re: Flow of Electrons in a DC Circuit
« Reply #21 on: March 24, 2017, 05:10:29 pm »
Brumby,

Just because I don't agree with you does not mean I dismissed it out of hand.  That is being presumptuous.

Correcting wrong thinking and incorrect perceptions is not going to cause the beginner to become so confused and bemused that s/he cannot learn further or function.  They can either ignore me or ask for more clarification.

Yes, I said that charge does not flow twice.  Is that fact going to drive the student over the edge?

I would hope that the training for the high jump would consist of more that just handing someone a long pole and saying "Go do it".

You can train a monkey to make something.  But a human will understand better what s/he made if s/he knows the basic principles of what he did.  S/he will be challenged.

I believe you are wrong about not teaching students the right way the first time.  A good argument can me made that reinforcing the wrong way does more harm than good. 

To the OP:  Can you say something about about the way I answered your question about current direction?  Did you walk around dazed and disoriented afterwards?  Any comments will be welcome.

Ratch

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Offline Ratch

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Re: Flow of Electrons in a DC Circuit
« Reply #22 on: March 24, 2017, 05:12:58 pm »
The poor guy who started this thread is probably more confused now than he was to begin with.

I asked him to respond to that question in a previous post.  I hope he does.

Ratch
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Offline rstofer

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Re: Flow of Electrons in a DC Circuit
« Reply #23 on: March 24, 2017, 05:48:04 pm »
The good news is that we can drive a car without taking Thermodynamics!

Same with 'current flow'.  Yes, there are better terms and yes, there are more precise (but not necessarily better) explanations but they aren't needed to get a diode to work.  You can go a long way by just assuming <whatever you want to call it> is flowing from plus to minus.  In the meantime, while folks debate <what to call it> I'll just stick with 'current flow'.


 
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Offline suicidaleggroll

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Re: Flow of Electrons in a DC Circuit
« Reply #24 on: March 24, 2017, 06:35:32 pm »
Long ago, "current" was defined as the flow of positive charge.  That's what the word "current" means, that's how diagrams are drawn, that's how components are labeled, etc.  It makes no difference whether the charge carrier in the real world is actually positive or negative, that changes nothing when it comes to designing/building circuits.  "Current" is the flow of positive charge, it moves from positive to negative, end of story.
 
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