electric current
- Thread starter eddy212
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Please don't take this as being anything less than encouragement. But I think it is possible that you do not understand the question you are asking well enough to understand the answer yet.
What I mean is that there are several ways of describing what happens inside a wire. None are completely and precisely accurate; none are absolutely wrong. What you need to do is to make sure you know how the question is being asked, so that you can tell what the person asking the question is trying to get as the "correct answer."
Here is a bit of truth. The things that move within a wire are electrons. Because of a choice, a "flip of the coin" kind of choice, alleged to have been made by Benjamin Franklin, the type of charge assigned to an electron is the one called "negative." So one way to answer the question is that "current" is negative, because it is electron flow.
Here's another bit of truth. If an electron moves from its "home atom" to an atom on its left, and if it therefore appears as though negative charge has moved to the left, you must also realize that the atom it left behind now has a net "plus one" positive charge. This absence of an electron is called, please forgive the originator of this term, a "hole." It is equally proper to describe this situation by saying current is positive, because the "hole" has moved to the right.
So which is the "real" truth? Is current a negative thing moving to the left, or is current a positive thing moving to the right? You might as well ask, which of the following statements represents the "real truth": statement one, "the grass is green," or statement two, "the sky is blue." The reality of the situation is that both can be, and are true, and neither contradicts the other.
When I went to college, I was taught electricity in terms of the flow of positively charged "holes." This is know as "conventional current." Then, when I joined the Navy, I was taught electricity in terms of the flow of negatively charged electrons. I do not know if this version has an official name. Which is true? Both. Which answer is your instructor looking for? You have to get your instructor to clarify the question.
What I mean is that there are several ways of describing what happens inside a wire. None are completely and precisely accurate; none are absolutely wrong. What you need to do is to make sure you know how the question is being asked, so that you can tell what the person asking the question is trying to get as the "correct answer."
Here is a bit of truth. The things that move within a wire are electrons. Because of a choice, a "flip of the coin" kind of choice, alleged to have been made by Benjamin Franklin, the type of charge assigned to an electron is the one called "negative." So one way to answer the question is that "current" is negative, because it is electron flow.
Here's another bit of truth. If an electron moves from its "home atom" to an atom on its left, and if it therefore appears as though negative charge has moved to the left, you must also realize that the atom it left behind now has a net "plus one" positive charge. This absence of an electron is called, please forgive the originator of this term, a "hole." It is equally proper to describe this situation by saying current is positive, because the "hole" has moved to the right.
So which is the "real" truth? Is current a negative thing moving to the left, or is current a positive thing moving to the right? You might as well ask, which of the following statements represents the "real truth": statement one, "the grass is green," or statement two, "the sky is blue." The reality of the situation is that both can be, and are true, and neither contradicts the other.
When I went to college, I was taught electricity in terms of the flow of positively charged "holes." This is know as "conventional current." Then, when I joined the Navy, I was taught electricity in terms of the flow of negatively charged electrons. I do not know if this version has an official name. Which is true? Both. Which answer is your instructor looking for? You have to get your instructor to clarify the question.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Oh, and I just noticed something about the way you worded your question. Please let me clarify that "current" is not just "charge." Rather, "current" is "charge in motion," or you might say "the flow of charge." An electron is not current, but an electron moving to the left is current. A "hole" is not current, but a "hole" moving to the right is current.
hole vs. electron flow
hole vs. electron flow
Instead of assigning a "charge" to the current flow, think of electric current as an organized migration of electrons from atom to atom in a conductor due to the influence of a source of energy. Current in amperes is defined as 6.25*10^18 electrons passing any given point every second. In defining electric current, I have found most people indintify with the flow of something (electrons) as opposed to the flow of an absense of something (holes).
Regardless of how one chooses to define current flow, it is worth noting that the quatity of charge is still measured in coulombs and defined as amperes. Essentially for every forward motion of each electron there is a corresponding backward motion of a hole; the rates are both the same.
Conventional flow (hole flow) is utilized in most engineering books today because of the compatibility with semiconductor technology. The symbol for a diode, as an example, shows the direction of the arrow as being conventional current flow. But the flow of electrons originates from the negative side of the diode flowing to the postive side; against the direction of the arrow!
Anyway, I guess I let my electronics engineering days get the best of me on this topic, but I find it rewarding to discuss and listen to various points of view.
Rich
hole vs. electron flow
eddy212 said:
Instead of assigning a "charge" to the current flow, think of electric current as an organized migration of electrons from atom to atom in a conductor due to the influence of a source of energy. Current in amperes is defined as 6.25*10^18 electrons passing any given point every second. In defining electric current, I have found most people indintify with the flow of something (electrons) as opposed to the flow of an absense of something (holes).
Regardless of how one chooses to define current flow, it is worth noting that the quatity of charge is still measured in coulombs and defined as amperes. Essentially for every forward motion of each electron there is a corresponding backward motion of a hole; the rates are both the same.
Conventional flow (hole flow) is utilized in most engineering books today because of the compatibility with semiconductor technology. The symbol for a diode, as an example, shows the direction of the arrow as being conventional current flow. But the flow of electrons originates from the negative side of the diode flowing to the postive side; against the direction of the arrow!
Anyway, I guess I let my electronics engineering days get the best of me on this topic, but I find it rewarding to discuss and listen to various points of view.
Rich
In the late 50s it was all "electron flow". The math matches up with tubes pretty good.
In the 60s, transistors hit, but they were all germainium(sp?) PNP and electron flow against the arrow still worked well.
Then in the 70, silicon NPN became dominate and now "current flow", defined as "positive to negative" fit the concepts and math.
Not too long after, complimentary NPN, PNP silicon hit the market. Now both conventions work.
As for your question, either one works, the math is the same. I think it was Bob Alexander that explained it the best. My translation is, "It's a pseudo-vector. There is no physical direction. It is the direction you assign."
Some say, "Well when I went to school it was 'electron flow', negative to positive" Others say, "For me it was 'current flow', positive to negative." My response is, "I don't care. Tell me what direction you like, and I'll set up the math to fit. Answers will be the same."
The wind is almost a good analogy. You can't see it, but you can see and measure the effects - same thing for electricity. The difference is the wind has a physical direction - you can point the direction it is blowing.
I really get a kick out of the ones that say something on the order of, "Well, as I see it, on a sub-atomic level, the positrons circulate anti-clockwise around the flux capacitor." I've never said so, but my thoughts are, "Gee, I don't have a sub-atomic meter and I don't deal with single positrons, (or electrons) - generally it is on the order of a kazillion or so. Just be sure your concepts of positron circulation don't run afoul of the mathematical model."
My theory: I don't pretend to understand the atomic level physics. Don't need to, don't want to. The mathematical model is the part I am interested in. It is repeatable and accurate. Understand the model and it's limitations, and you have the concepts forever.
Standing down from my soapbox now - thank you for listening
In the 60s, transistors hit, but they were all germainium(sp?) PNP and electron flow against the arrow still worked well.
Then in the 70, silicon NPN became dominate and now "current flow", defined as "positive to negative" fit the concepts and math.
Not too long after, complimentary NPN, PNP silicon hit the market. Now both conventions work.
As for your question, either one works, the math is the same. I think it was Bob Alexander that explained it the best. My translation is, "It's a pseudo-vector. There is no physical direction. It is the direction you assign."
Some say, "Well when I went to school it was 'electron flow', negative to positive" Others say, "For me it was 'current flow', positive to negative." My response is, "I don't care. Tell me what direction you like, and I'll set up the math to fit. Answers will be the same."
The wind is almost a good analogy. You can't see it, but you can see and measure the effects - same thing for electricity. The difference is the wind has a physical direction - you can point the direction it is blowing.
I really get a kick out of the ones that say something on the order of, "Well, as I see it, on a sub-atomic level, the positrons circulate anti-clockwise around the flux capacitor." I've never said so, but my thoughts are, "Gee, I don't have a sub-atomic meter and I don't deal with single positrons, (or electrons) - generally it is on the order of a kazillion or so. Just be sure your concepts of positron circulation don't run afoul of the mathematical model."
My theory: I don't pretend to understand the atomic level physics. Don't need to, don't want to. The mathematical model is the part I am interested in. It is repeatable and accurate. Understand the model and it's limitations, and you have the concepts forever.
Standing down from my soapbox now - thank you for listening
Mathematical explanation
Mathematical explanation
Here is a good site for a mathematical view of semiconductors... ...for those of you who enjoy this type of thing. I used it frequently in a semiconductor course last semester.
http://ece-www.colorado.edu/~bart/book/book/title.htm
Enjoy.
Matt
Mathematical explanation
Here is a good site for a mathematical view of semiconductors... ...for those of you who enjoy this type of thing. I used it frequently in a semiconductor course last semester.
http://ece-www.colorado.edu/~bart/book/book/title.htm
Enjoy.
Matt
Shockedby277v
Senior Member
- Location
- Michigan
There are two theories. The conventional current flow theory and the electron current flow theory. The conventional current flow theory was thought to be that electrons moved from positive to negative. And then theres the todays theory, the electron flow theory which the electrons flow from negative to positive. Both are still used today, so you need to find out which is needed.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
No. "Conventional current" is the flow of positively charged "holes" in the direction from positive to negative. An electron cannot flow toward negative, as you may recall from the "Like Charges Repel" rule.Shockedby277v said:
Both of the "theories" you named are precisely the same, as viewed from outside the wire. It is not possible for an ammeter to tell the difference between a positive charge moving to the right and a negative charge moving to the left.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Slight disagreement:
"conventional current flow" is simply considering that positive _charges_ move from positive to negative. The positive charges could be "holes", or they could be protons or positrons.
I quite agree, an ammeter can't tell the difference between a flow of electrons from left to right, or a flow of protons from right to left. Note, however, that these are two different things, and you could tell them apart if you introduced a magnetic field perpendicular to the current flow (Hall Effect).
-Jon
"conventional current flow" is simply considering that positive _charges_ move from positive to negative. The positive charges could be "holes", or they could be protons or positrons.
I quite agree, an ammeter can't tell the difference between a flow of electrons from left to right, or a flow of protons from right to left. Note, however, that these are two different things, and you could tell them apart if you introduced a magnetic field perpendicular to the current flow (Hall Effect).
-Jon
Jon - I have to agree with charlie (don't panic charlie, it's okay I'm not seeing some of the things you are saying.
If you are talking about the mag field around the outside of the conductor caused by the moving charged particles, then I don't see any difference in the mag field that would depend on the charge carrier.
At the level we deal with the physical phenomena (non-particle physicists level) and the instrumentation we commonally or even uncommonally use (which would exclude cloud chambers, particle accelerators, and positronic flux capacitors), I don't see what we could measure that would tell us the difference.
I'm not seeing some of the things you are saying.Okay that seems true.winnie said:
Starting to lose understanding here. Are you saying you want to add an external magnetic field crossways to the conductor, like with permanent magnets. Then a moving charged particle in a magnetic field will deflect. If so, the charged particles are contained with in a conductor. How are they going to deflect out of the conductor. Also, what would we measure this with?winnie said:
If you are talking about the mag field around the outside of the conductor caused by the moving charged particles, then I don't see any difference in the mag field that would depend on the charge carrier.
At the level we deal with the physical phenomena (non-particle physicists level) and the instrumentation we commonally or even uncommonally use (which would exclude cloud chambers, particle accelerators, and positronic flux capacitors), I don't see what we could measure that would tell us the difference.
Current is not a vector
Current is not a vector
Winnie is quite correct with the Hall Effect explanation.
Current is defined as I = dQ/dt. This definition does not give any reference to the polarity of the charge, or direction along any conductor. We always assume the direction of current to be along a certain conductor. Taking this into consideration, we can see that current is not a vector... ...it has been said that current is a pseudo-vector in a previous post. I like this notion. So I agree with the idea that you should pick a convention and stick with it for whatever you are doing. As an electrician, I used the "electron flow" theory, and as an EE, I will use conventional theory.
You will get the correct answers either way, then you generally use common sense for the rest!
-Matthew
Current is not a vector
Winnie is quite correct with the Hall Effect explanation.
Current is defined as I = dQ/dt. This definition does not give any reference to the polarity of the charge, or direction along any conductor. We always assume the direction of current to be along a certain conductor. Taking this into consideration, we can see that current is not a vector... ...it has been said that current is a pseudo-vector in a previous post. I like this notion. So I agree with the idea that you should pick a convention and stick with it for whatever you are doing. As an electrician, I used the "electron flow" theory, and as an EE, I will use conventional theory.
You will get the correct answers either way, then you generally use common sense for the rest!
-Matthew
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
winnie said:
No, they are holes, not protons, and not positrons (or at least, not in a wire). It was recognized long ago that the thing that moves is the negatively charged electrons. But the use of positive current was so thoroughly engrained that the decision was made to model the actual physical condition with the equivalent, though non-physical, "hole."
As to a detector based on the Hall Effect, I submit that it could not discern the difference between an electron moving left and a positron moving right (if such a thing could happen in a wire). The magnetic field imposed by the detector would force the moving electron one way (i.e., to one side of the wire), and it would force a moving positron the other way (i.e., to the other side of the wire). So when the detector looks for the resultant electric field across the wire, it will see the same amount of field in the same orientation.
Hall Effect
Hall Effect
Here is some good material on the Hall Effect for the interested! Of course this is for semiconductor material, and I dont know how the interaction takes place in the intermingling bandgaps of metals... ...but I think it should still be the same
http://ece-www.colorado.edu/~bart/book/book/chapter2/pdf/ch2_7_5.pdf
Enjoy.
-Matthew
Hall Effect
Here is some good material on the Hall Effect for the interested! Of course this is for semiconductor material, and I dont know how the interaction takes place in the intermingling bandgaps of metals... ...but I think it should still be the same
http://ece-www.colorado.edu/~bart/book/book/chapter2/pdf/ch2_7_5.pdf
Enjoy.
-Matthew
Last edited:
Shockedby277v
Senior Member
- Location
- Michigan
charlie b said:
I dunno, that's what I have learned and almost quoted word for word from holt's book of theory. I do understand that it is basic theory and there is so much more to it. I'm still learning.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
charlie b said:
I aboslutely agree that in a metal wire, or even in a semiconductor, what is moving is electrons, either electrons in one direction, or holes in the opposite direction.
I wanted to amplify the point that the net current flow is all that matters as far as the current measured by an ammeter. This remains true even if the electric current flow is not in wires at all, for example positive ions flowing in solution, or a beam of protons in a particle accelerator; these still carry current, and the net current measured by an ammeter will be the same.
charlie b said:
I think that the diagrams in the link by mpross show the basic asymmetry here. Also see this article on 'Lorenz force' http://en.wikipedia.org/wiki/Lorentz_Force The force on a charged particle moving in a magnetic field is perpendicular to both the velocity of the particle and the magnetic field. The force is proportional to the velocity, the charge, and the magnetic flux. The sign of the force on an electron is equal and opposite to the sign of the force placed on an equal positive in the same circumstances.
Say that I have conventional current flowing from left to right in a conductor, and a magnetic field that cuts across the conductor, flowing 'into' the page. If the current is positive 'holes' moving from left to right, then in the magnetic field these 'holes' will experience a force 'upward', and the 'top' side of the conductor will be rendered more positive than the bottom side.
Now consider if the current were electrons flowing from right to left. The charge of the particles is reversed, the direction of travel is reversed, but the magnetic field is the same. The net result is that the electrons experience a force upward, and the 'top' side of the conductor is rendered more _negative_ than the bottom side.
In metallic conductors the voltage developed is quite small, but in semiconductors this 'hall voltage' (voltage measured perpendicular to the flow of current in the presence of a magnetic field) is significant, and its sign depends on weather the semiconductor is N type or P type.
-Jon
Very interesting...
I once found a old book (1800's) at the dump (not scavenging, just dumping some trash) that had a section on electricity and batteries. I've since given the book away, but I remember one "experiment" where the scientist had connected one electrode to a dog's head and inserted the other into his rectum (true story). Needless to say, when the switch was closed old Rover bit the dust. I'm not sure what the voltage was (neither did the scientist I think). This was hailed as a great discovery in the book. I wonder if 100 years from now (or 2525 if man is still alive) if someone will look at present day science and think about how immature man was in his understanding of electricity.
Sorry to interrupt a very informative post, but I thought I'd lighten things up a bit.
steve
I once found a old book (1800's) at the dump (not scavenging, just dumping some trash) that had a section on electricity and batteries. I've since given the book away, but I remember one "experiment" where the scientist had connected one electrode to a dog's head and inserted the other into his rectum (true story). Needless to say, when the switch was closed old Rover bit the dust. I'm not sure what the voltage was (neither did the scientist I think). This was hailed as a great discovery in the book. I wonder if 100 years from now (or 2525 if man is still alive) if someone will look at present day science and think about how immature man was in his understanding of electricity.
Sorry to interrupt a very informative post, but I thought I'd lighten things up a bit.
steve
The simple answer, eddy212, is neither. Current is measure of the flow of electrons (not "holes"... they do not move [by relative comparison], even in a destructive anode/cathode relationship). A positive charge is where there is a shortage of neutralizing electrons in the conductive material, and a negative charge is where there is an overabundance. Conductance can take place between any two dissimilarly charged sources--positive-positive, positive-negative, and negative-negative--if there is a conductive path for the electrons to move from one to the other.
- Status