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Help! Conventional Flow Vs Electron Flow

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electric_n00b

New Member
I have read many things and tried to understand this many times. At first I think I understand but by the end of the explanation I always end up confused. :D

I understand that, in conventional flow notation, using a + symbol is technically inaccurate as, in physics, electrons are said to have a negative charge. It would be very helpful if you could tell me if I'm right or wrong about the following:


Q: If I have a simple schematic of a DC circuit, using a 9v battery, that is drawn using conventional flow notation would I be correct in assuming the following:

- The terminal marked + on the battery connects to the circuit at the point where the + terminal is marked in the schematic.

- The actual "real world" direction of flow of the electrons is from the terminal marked + in the schematic and on the battery. To to the terminal marked - in the schematic and on the battery.

- To generalise: In real life, polarized components having terminals marked with + and - symbols indicate that the real world direction of flow of electrons goes from the + terminal to the - terminal.
 

crutschow

Well-Known Member
Most Helpful Member
Conventional (current) flow is from + to -. It comes from early times when no one knew the charge of the current carriers and so they arbitrarily defined them as being positive.

But the current carriers turned out to be electrons, which are negatively charged, and since like charges repel and opposite charges attract, they are attracted to a plus terminal. Thus electrons flow from minus to plus.
 

dknguyen

Well-Known Member
Most Helpful Member
The polarities are still correct. Electrons (- charge) flow from the - terminal of the battery through the circuit to + terminal of the battery.
Direction of Current
Electron Flow

When we say "current flows from + to -", we do NOT mean electron flow. We mean conventional current flow or "hole" flow. Do you know the concept of electrons and holes? We know positive charges come from protons and negative charges come from electrons. But we also know that protons do not flow since the proton is stuck in the nucleus, therefore positive charges do not physically flow. Electrons on the other hand, do flow since they can jump from atom to atom so negative charges can flow. But when the negative charge jumps, it leaves behind a "hole" of positive charge that originates from the proton in the nucleus which no longer has it's charge cancelled to zero because the electrons isn't there anymore. As the electrons move in one direction and leave behind holes, it will appear as though the holes flow in the opposite direction. This hole flow is conventional current.
Hole Flow

This is probably the worst legacy issue I hate about electronics, luckily it doesn't matter most of the time until you get into semiconductor physics.
 
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Sceadwian

Banned
You'll almost never see electron flow used, unless as you say you're a physicist.
 

electric_n00b

New Member
Conventional Flow:
Energy flows from + to -

Electron Flow:
Energy flows from - to +

MSPaint Representation:
Thanks, what I'm having trouble with is which direction the electrons are travelling in reality and relating it to the schematic.

For example: If you hooked up a battery to a circuit the way it is in the diagram you posted which direction would the electrons actually be flowing?
 

dknguyen

Well-Known Member
Most Helpful Member
In reality the electrons are following the blue arrows. Think about it this way, the polarity symbols indicate the type of charge carrier (an electron or a hole) that originates from the terminal. Electrons are negative, so they come out of the negative terminal following the blue line.

Exactly what the picture says. Perhaps if you put your confusion into words we clear up that particular confusion. I thought the picture was pretty obvious so we must be missing something from your train of thought
 
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Sceadwian

Banned
"Conventional flow" Is from + to -
"Electron flow" is from - to +

I'm just repeating what Parkinglotlust said, he was pretty clear. Why are you asking the question again?
 

dknguyen

Well-Known Member
Most Helpful Member
I think you are confusing the fact that an electron is "something" but has a "negative" charge. Normally we are used to the idea of "something" flowing to an area of "nothing". In math this intuitively starts out as "positive" to "negative" since positive is more of something than negative.

BUt when electronics started out we weren't able to see what was "something" and what was "nothing" so we made an exectuve decision and labelled one positive and one negative without knowing for sure. It turns out we made a mistake and reversed the labels we are normally used to. So "something" which is labelled "negative" flows towards "nothing" which is labelled "positive". Positive and negative are purely mathematical labels, you could reverse everything and the meaning would not change.

It's a bit like knowing that dark and light exist, but not knowing whether empty space is normally dark or light, and whether it was dark beams darkening or light beams lighting. One has to be nothing, one has to be something, but you're not sure which. If you were sure, you would give "something" the label positive and the "nothing" negative. If you weren't sure but had no choice, you just give randomly give them a label and hope you're right. We were not right in this case.

Did you read the 3 links I sent you? Or more importantly, look at the animations?
 
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electric_n00b

New Member
Conventional (current) flow is from + to -. It comes from early times when no one knew the charge of the current carriers and so they arbitrarily defined them as being positive.

But the current carriers turned out to be electrons, which are negatively charged, and since like charges repel and opposite charges attract, they are attracted to a plus terminal. Thus electrons flow from minus to plus.
Thanks. So, if you are building a simple circuit from a schematic in conventional flow notation you would connect polarized components as they are marked on the component and on the chematic. i.e. the terminal marked + on capacitor would connect to the point in the schematic where the + terminal of the capacitor symbol is?

The polarities are still correct. Electrons (- charge) flow from the - terminal of the battery through the circuit to + terminal of the battery.
Direction of Current
Electron Flow

When we say "current flows from + to -", we do NOT mean electron flow. We mean conventional current flow or "hole" flow. Do you know the concept of electrons and holes? We know positive charges come from protons and negative charges come from electrons. But we also know that protons do not flow since the proton is stuck in the nucleus, therefore positive charges do not physically flow. Electrons on the other hand, do flow since they can jump from atom to atom so negative charges can flow. But when the negative charge jumps, it leaves behind a "hole" of positive charge that originates from the proton in the nucleus which no longer has it's charge cancelled to zero because the electrons isn't there anymore. As the electrons move in one direction and leave behind holes, it will appear as though the holes flow in the opposite direction. This hole flow is conventional current.
Hole Flow

This is probably the worst legacy issue I hate about electronics, luckily it doesn't matter most of the time until you get into semiconductor physics.
Oh my god! Thank you so much! I think you have just hit the nail on the head and made me see where the flaw in my understanding occurs. The notion of current flow being different from that of electron flow! I need to investigate this further.

You'll almost never see electron flow used, unless as you say you're a physicist.
So it's safe to assume that, unless specified otherwise, all schematics are marked in conventional notation and real life polarized components are marked + & - so as to connect those terminals to the points marked with the same + or - in the schematic.
 

steveB

Well-Known Member
Most Helpful Member
This is probably the worst legacy issue I hate about electronics,
I've heard that we have Ben Franklin to thank for this. You know, he was really amazing and did so many great things in his life. But, apparently he wasn't much of a gambler. He had a 50% chance and he got it wrong! :)

I'll bet there exists a parallel universe made of antimatter with positrons flowing in conductors. I wonder, did the people there define it the opposite way, and get it wrong too? :confused:
 
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electric_n00b

New Member
EDIT: I have been replying to posts but keep getting a "message will be checked by moderators" message which is making it hard to have a conversation!


dknguyen, this is the 3rd time I've tried to thank you. I think you have hit the nail on the head in the flaw in my understanding. That being the notion of charge flow is not the same as electron flow!


In reality the electrons are following the blue arrows. Think about it this way, the polarity symbols indicate the type of charge carrier (an electron or a hole) that originates from the terminal. Electrons are negative, so they come out of the negative terminal following the blue line.

Exactly what the picture says. Perhaps if you put your confusion into words we clear up that particular confusion. I thought the picture was pretty obvious so we must be missing something from your train of thought

My confusion is like this:

When I look at a schematic to try and figure out what is going on I imagine a physical flow of electrons running through a circuit from the positive terminal of the battery to the negative terminal of a battery.

From what you have said I am now getting the idea that this is wrong regarding the flow of electrons. But that it's correct to think of a more abstract notion of a "charge" flowing from the + to - terminals?

My electronics interest is in guitar amplifiers and effects. When polarized components such as diodes, capacitors, transistors and electron tubes are thrown in to the circuit it just confuses me.

For example, if I'm understanding what your saying then is this correct:

If you have a diode in a circuit a "charge" will be flowing from the + to - side but the actual electrons will be flowing from the - to + side?
 
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electric_n00b

New Member
The polarities are still correct. Electrons (- charge) flow from the - terminal of the battery through the circuit to + terminal of the battery.
Direction of Current
Electron Flow

When we say "current flows from + to -", we do NOT mean electron flow. We mean conventional current flow or "hole" flow. Do you know the concept of electrons and holes? We know positive charges come from protons and negative charges come from electrons. But we also know that protons do not flow since the proton is stuck in the nucleus, therefore positive charges do not physically flow. Electrons on the other hand, do flow since they can jump from atom to atom so negative charges can flow. But when the negative charge jumps, it leaves behind a "hole" of positive charge that originates from the proton in the nucleus which no longer has it's charge cancelled to zero because the electrons isn't there anymore. As the electrons move in one direction and leave behind holes, it will appear as though the holes flow in the opposite direction. This hole flow is conventional current.
Hole Flow

This is probably the worst legacy issue I hate about electronics, luckily it doesn't matter most of the time until you get into semiconductor physics.
I replied to three posts before but got a message like "the message will be approved by moderators first"...


Anyway, I'll repeat what I said.

Thank you so much, I think you have hit he nail on the head where the flaw in my understanding is: This notion of a charge flowing in the opposite direction to what the physical electron flow is.

I am digesting all the info and links you posted. I think I may be getting close to having an epiphany now. :D
 

dknguyen

Well-Known Member
Most Helpful Member
My confusion is like this:

When I look at a schematic to try and figure out what is going on I imagine a physical flow of electrons running through a circuit from the positive terminal of the battery to the negative terminal of a battery.

From what you have said I am now getting the idea that this is wrong regarding the flow of electrons. But that it's correct to think of a more abstract notion of a "charge" flowing from the + to - terminals?
No abstract notion is needed if you understand the difference between the appearance of something flowing and the fact that something physically is flowing. Your notion of charge in this case is holes which occur because of the positive charge of protons in the atom's nucleus, but the protons are not moving themselves because they are stuck in the nucleus. BUt the positive they generate *appears* to be flowing in the opposite direction of the electrons which cancel out their positive charge as they moving. See the 3 links I provided in my first post. THey provide more details and graphics.

If you have a diode in a circuit a "charge" will be flowing from the + to - side but the actual electrons will be flowing from the - to + side?
Correct. YOur difficulty arises from your association with "positive" as something and "negative" as nothing (see my previous post).
 
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Sceadwian

Banned
electric noob, you have the totally wrong idea of how electron flow occurs at all. It takes minutes, hours, months, even years for a single electron to actually move from one end of a circuit to the other in a metal, and in the case of AC circuits the electrons don't actually move at all on average, what moves is the energy. Far too often people think of electronics as water flowing from one point to another, which it absolutely is not. It's energy (like a wave in water) traveling from one point to another, with electronics electrons are the media, what is being 'transferred' is energy.

Read this page
SCIENCE HOBBYIST: how transistor works, an alternate viewpoint
It's a lot to take in but explains it all.
 

electric_n00b

New Member
Correct. YOur difficulty arises from your association with "positive" as something and "negative" as nothing (see my previous post).
electric noob, you have the totally wrong idea of how electron flow occurs at all. It takes minutes, hours, months, even years for a single electron to actually move from one end of a circuit to the other in a metal, and in the case of AC circuits the electrons don't actually move at all on average, what moves is the energy. Far too often people think of electronics as water flowing from one point to another, which it absolutely is not. It's energy (like a wave in water) traveling from one point to another, with electronics electrons are the media, what is being 'transferred' is energy.

Read this page
SCIENCE HOBBYIST: how transistor works, an alternate viewpoint
It's a lot to take in but explains it all.
Thank you so much guys! You won't believe how much help what you are saying is to me. It's much appreciated.

dknguyen, I think you nailed what the flaw in my understanding is. The notion of "charge" flowing and not electrons flowing. I feel like I'm on the verge of a personal breakthough in understanding now!
 

MrAl

Well-Known Member
Most Helpful Member
Hello there,


It is not correct physically to think of electrons as flowing from the
positive terminal of the battery, through the circuit, and back to the
negative terminal because that is not the way it works in reality.
It is however correct to think of the 'holes' as flowing in this way
because the hole flow is opposite to the electron flow as shown in
the accompanying diagram.
The convention of current flowing from positive, through the circuit,
and back to the negative has been accepted however not only because
it was invented a long time ago but because it simplifies a lot of
analysis by eliminating the minus sign (-) that would have to be
present in a lot of formulas where you could leave it out if you assume
'conventional' current flow (positive to negative).
For example, Ohms Law:
R=V/I
if we had negative current flow would read:
R=V/(-I), or R=-V/I
either of which makes things more difficult.
This is also true in other areas such as control theory and design.
Using the convention of current flow from positive to negative results
in simpler formulas.
In physics electron flow results in simpler formulas rather than 'conventional'
current flow so it really depends on what area we are working in.

What you are looking for i think is how to relate the various parts you
find to the circuits and how they connect together properly, and to
understand more about this so that you can look at a schematic and
understand how and why the component is connected the way it is,
and also to be able to duplicate this yourself with an actual circuit
breadboard you build up at home.
To do this you really need to take one type of component at a time
and look at it carefully, and fully understand it before moving to the
next.
Start with a resistor, which im sure you know is not polarized, so you
can connect it into the circuit either way you want to.
A diode however does have a polarity, so you have to be careful how
you connect that into a circuit. Well, if you look at the diode you
will see that it looks a lot like an arrowhead. The arrowhead points
in the direction of *conventional current flow* (positive to negative)
so that in order to get the diode to conduct you have to connect
the anode (tail of the arrowhead) to the positive terminal of a battery
and the cathode (tip of the arrowhead) to the negative terminal of
a battery (though a resistor to limit current). The current would then
flow from the positive terminal of the battery, to the anode of the
diode, through the diode to the cathode, then through the resistor
and finally back to the negative terminal of the battery. Again,
this is 'conventional' current flow and is more like what is called
'hole' flow than actual electron flow, but nonetheless works out in
practice when thinking about it in this manner.

If we wanted to look at the diode in terms of true electron flow, we would
simply start at the negative terminal of the battery, move to the
resistor, through the resistor, then to the cathode of the diode and
through the diode to the anode, then through the wire back to the
positive terminal of the battery. The direction we choose is rather
arbitrary unless we are reading material that already assumes a type
of current flow, in which case we then are forced to adapt to whatever
that author chose to use at the time of writing. It's a good idea then
to know both ways of looking at a circuit.

When connecting one circuit to another or a battery to a circuit,
usually there is only one convention however. That is to 'match' up
the polarities to one another. Thus, to connect a battery to a circuit
that has plus (+) and minus (-) written or labeled on it, we would
connect the positive terminal of the battery to the plus (+) and the
negative terminal of the battery to the minus (-).

How we connect other things depend on how we want to connect them
together, such as in series or parallel. You probably need to look at these
kinds of basic circuit connections also before anything else.

Here is a diagram of current flow looking at it from the point of view
of an electron or of a hole...
 

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Leftyretro

New Member
Electric_noob;

Don't try and think too hard on this, it will just give you a headache. You should have a concept that something flows in one direction in DC circuits (the something flows back and forth in AC circuits!), as when you open a switch contact nothing can flow and when you close it flow is possible.

In the early days of electricity discoveries they decided by fiat or consensus (who know for sure!) that current flow is from + to -. They didn't at the time have the knowledge of atoms and their structure let alone how current could flow through them, but they did understand that flow would happen when there was a voltage potential difference between conducting nodes.

So the scientist of the day said current flows from positive to negative. It's still taught that way in college engineering schools, but in technical, military and other practical studies they teach electron flow which is - to +. It doesn't really matter which way one thinks current flows as long as they are consistent with their thinking.

The weird part is that the engineering types, not wanting to admit that their original definition of current flow direction was wrong, went and invented 'hole flow' theory to somehow justify the original error. Sad part is that the engineering types get to define the arrow direction used in drawing semiconductor symbols so that's why all the arrows point backwards to true electron current flow. ;)

Lefty
 
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crutschow

Well-Known Member
Most Helpful Member
This is probably the worst legacy issue I hate about electronics, luckily it doesn't matter most of the time until you get into semiconductor physics.
It also was important (and still may be for the few people that still use them) in understanding the operation of a vacuum tube. Electrons boil off the hot cathode, fly through the tube vacuum, and are collected by the positive polarity plate. It doesn't make much physical sense if you try to talk about positive charges leaving the plate and going to the cathode.
 

Leftyretro

New Member
It also was important (and still may be for the few people that still use them) in understanding the operation of a vacuum tube. Electrons boil off the hot cathode, fly through the tube vacuum, and are collected by the positive polarity plate. It doesn't make much physical sense if you try to talk about positive charges leaving the plate and going to the cathode.
You mean holes can't flow in a vacuum? If electrons can flow in a vacuum why can't those new fangled holes also. ;)

Lefty
 
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