Hello, not sure I have the correct forum but..

I have a question that I cannot seem to find a logical answer to aside from someone giving me a better defenition of "current".
Electron flow basically states that electrons flow from negative to positive. But, current is said to flow from positive to negative...

If you look up the defenition of "current" it is a measure of the flow of electrons. If it is a measure of the flow of electrons and electrons are moving negative to positive, how is current moving positive to negative?

 

This question is raised ad nauseam. You might like to peruse the various past threads on the AAC Forums that have been devoted to the topic.

There's even a current thread that has associations ....

http://forum.allaboutcircuits.com/showthread.php?t=86150

 

The direction of current was initially arbitrarily defined with the charge carriers assumed to be positive particles and the current direction from positive to negative. It was later determined that the carriers (electrons) actually had a negative charge so the electron flow direction is opposite the "current" flow direction.

So whether you use current flow or electron flow to describe a circuit operation is up to you. As long as you are consistent, the calculated results will be the same. The only time you need to use electron flow is when describing the internal operation of electron tubes or solid-state devices.

I use current flow because I find it easier to think of flow from positive to negative. Also the arrows on diodes and transistors point in the forward biased direction of current flow, which makes it easier for me to understand a circuit's operation. And most circuits with one supply, have a positive supply so the normal current flow is from the top (the power) to the bottom (ground) on a schematic.

 

Hello, not sure I have the correct forum but..

I have a question that I cannot seem to find a logical answer to aside from someone giving me a better defenition of "current".
Electron flow basically states that electrons flow from negative to positive. But, current is said to flow from positive to negative...

Way back in early days, somebody took a guess and got it WRONG.

 

Hello, not sure I have the correct forum but..

I have a question that I cannot seem to find a logical answer to aside from someone giving me a better defenition of "current".
Electron flow basically states that electrons flow from negative to positive. But, current is said to flow from positive to negative...

If you look up the defenition of "current" it is a measure of the flow of electrons. If it is a measure of the flow of electrons and electrons are moving negative to positive, how is current moving positive to negative?

The proper definition of current is the flow of charge. In most cases, the charge carrier is the negatively charged electron, but not always.

The flow of a positive charge from positive to negative and the flow of a negative charge from negative to positive are identical and indistinguishable for most purposes (but not all purposes).

Consider the case of using electron flow and defining your current as going from negative to positive, say through a resistor connected across a 9V battery. If you have a 1kΩ resistor then the magnitude of the current is 9mA, or 9mC/s. But what about the sign? Well, your 9mC of charge that flow past a point each second are all negative, so your charge flow is -9mC/s or -9mA. So you have -9mA of current flowing from negative to positive. This is the same as 9mA of current flowing from positive to negative (again, unless you are working at a level in which the exact nature of the charge carrier matters).

So whether you work with conventional current or electron current, you have 9mA of current flowing from positive to negative or -9mA of current flowing from negative to positive. They are equivalent.

The people that want to claim that the "electron current" would 9mA from negative to positive are wanting to track the flow of electrons, which is fine, but then conveniently forget that the electron is negatively charged and fail to take into account the minus sign that goes along with that.

 

There is nothing inherently "negative" about an electron,& if the choice had been made the other way round back in the day,it would be positive.

We could have called positive & negative "Male & Female",or "Black & White".

The ways we can detect the presence of current are not charge carrier polarity sensitive.

A heating element for instance,doesn't care which way some imaginary +ve charge carriers flow,or which way electrons flow--it just gets hot!

It took about 3 minutes for first year Tech College students to understand the two concepts back in the day,but people are still agonising about them!

Rejoice,Conventional Current flow proponents!-----You have won the war!

Engineers all learn it that way!

 

We also have a dedicated section in the e-book: http://www.allaboutcircuits.com/vol_1/chpt_1/7.html

 

There should be absolutely no confusion between conventional and electron flow.

Electron flow describes the physical phenomenon.

Conventional flow is an accounting method used in calculating currents.

Both methods produce identical correct results.

Electron flow is the non standard way of computation and should be avoided.

 

There is nothing inherently "negative" about an electron,& if the choice had been made the other way round back in the day,it would be positive.

Sure. And if we had called the electron "positive" then the end of the battery that we now call the "positive" terminal would be called the "negative" terminal and, in my example, we would still have +9mA flowing from positive to negative or -9mA flowing from negative to positive. The name we choose for the polarity of the two types of charge dictates the names we use for voltage polarity with the net effect of multiplying both quantities by -1 and hence resulting in no change.

 

If you are a physicist, you will most likely think in terms of electrons and how they move or are affected by charged objects or magnetic fields.

If you are an engineer, then under most conditions you don't need to consider the electrons. You can work with "current" and "charge" and consider them both in their commonly used sense; we're aware that current is actually opposite to the way the electrons move, but it doesn't matter most of the time. The operation of a vacuum tube or a cathode-ray tube might force us to think about actual electrons and their behavior, but they're becoming historical relics. The photomultiplier tube is still in use, but it's a pretty specialized item.

 

I appreciate the responses but you guys have misunderstood my question. (my wording I'm sure)
I understand the difference between electron flow, conventional current flow and the history behind the two. However, when someone says "electrons flow negative to positive and current flows positive to negative" it hardly seems as they are discussing electron flow vs conventional. Hense the confusion...

 

Hello, not sure I have the correct forum but..

I have a question that I cannot seem to find a logical answer to aside from someone giving me a better defenition of "current".
Electron flow basically states that electrons flow from negative to positive. But, current is said to flow from positive to negative...

If you look up the defenition of "current" it is a measure of the flow of electrons. If it is a measure of the flow of electrons and electrons are moving negative to positive, how is current moving positive to negative?

So what is the question again?

 

Well, electrons are not the only charge carriers. Current may be composed by various components.

But, to be honest, in most beginner courses on physics, these details are not explained (nor should, in my opinion). Therefore, conflicts often appear.

If you want a solid explanation for all this mess, then start reading some semiconductor materials books and get a better grasp of how things work.

 

So what is the question again?

My instructors exact words. "Electrons flow from negative to positive. But, current flows from positive to negative."

I asked him about electron flow vs conventional theory and he then gave me several strange explanations making it seem if "current" were some particle other than an electron that flows positive to negative. (confused the hell out mme!)

 

Electrons are the charge carriers in metals and semiconductors.

There are positively charged particles that create current in other materials.
Hence "current flow" can be both positive and negative. Pay attention to the sign of the charge and the direction of flow.

When we talk about "conventional current flow" we are referring to a positive flow from a relatively positive potential to one that is less positive.

In semiconductor electronics, we frequently talk about electron-hole pair generation and recombination. The concept of positively charged holes is a meaningful way of describing semiconductor physics.

 

My instructors exact words. "Electrons flow from negative to positive. But, current flows from positive to negative."

I asked him about electron flow vs conventional theory and he then gave me several strange explanations making it seem if "current" were some particle other than an electron that flows positive to negative. (confused the hell out mme!)

How can you have a 'real' flow of electric current? Isn't it really a wave? You would have a slow 'drift', but I wouldn't consider that a current, and it would surely travel in the same direction as the electron flow?

Electrons drift quite slowly, I think. If you could dye one electron purple and watch it travel round a circuit, my understanding is that it would be travelling at about 1 metre per hour - and in the same direction as the electron flow...

 

Yes, if you multiply the charge of one electron by the number of electrons in a volume of material, and use that to figure out the average rate of travel of electrons in the material for a given current (i.e. motion of the charged particles) it is a surprisingly slow speed. But there are a lot of electrons!

 

Yes, if you multiply the charge of one electron by the number of electrons in a volume of material, and use that to figure out the average rate of travel of electrons in the material for a given current (i.e. motion of the charged particles) it is a surprisingly slow speed. But there are a lot of electrons!

Exactly. It's the rate at which the electrons pass a given point which gives the 'speed' of electricity. It's a bit like watching people going through the turnstile at a football match. They come through very quickly, and the turnstile is going round like crazy. But if you watch one person moving with the queue outside, they are moving very slowly. But the O.P's instructor seems to be saying that the queue is actually moving in the opposite direction!

 

I appreciate the responses but you guys have misunderstood my question. (my wording I'm sure)
I understand the difference between electron flow, conventional current flow and the history behind the two. However, when someone says "electrons flow negative to positive and current flows positive to negative" it hardly seems as they are discussing electron flow vs conventional. Hense the confusion...

It may not seem like it, but it is simply a discussion of electron flow versus conventional "current flow". If your instructor implied otherwise then he's not clear on the concept himself. There's no third alternate.

 

If you are a physicist, you will most likely think in terms of electrons and how they move or are affected by charged objects or magnetic fields.

If you are an engineer, then under most conditions you don't need to consider the electrons. You can work with "current" and "charge" and consider them both in their commonly used sense; we're aware that current is actually opposite to the way the electrons move, but it doesn't matter most of the time. The operation of a vacuum tube or a cathode-ray tube might force us to think about actual electrons and their behavior, but they're becoming historical relics. The photomultiplier tube is still in use, but it's a pretty specialized item.

Steam engines are historical relics,but the laws surrounding their operation are still valid.

"Conventional current flow" is not using "conventional"in the popular sense,as "usual",but in the sense of a "Convention",which is an agreed on usage.