[werd]

Which way do electrons flow?  Do they go positive to negative or vise versa? I only ask this since i heard a very interesting theory that voltage goes "neg to pos and current goes pos to neg". And they are measureable where voltage drops. Interestiing theory from an EE that  picked this up in university.

[JohnR]

Electrons are negatively charged, and thus "flow" from negative to positive. But they actually move very slowly, you'd be surprised.

No idea what "voltage goes neg to pos and current goes pos to neg" means.

[Mark Korda]

Hi Werd,electrons as we know always go from neg. to pos.I'm trying like you to grasp some of this stuff at 53.I got these old red and orange paper back books on e-bay that were used in the 50's to train Navy guys as fast as possible.In issue #1 it is stated in the early days of electronics,the( conventional current) was from positive to negitive,but that was wrong,an electron current goes from neg. to pos.(Basic Electricity by Van Valkenburg...Vol.1).....Hey Werd,I'm lost a little bit too.I went to summer school for math,and Ohms law is looking like a Marine boot camp obsticle....let me know..Mark Korda

[jimdgoulding]

Electrons are negatively charged, and thus "flow" from negative to positive. But they actually move very slowly, you'd be surprised.

No idea what "voltage goes neg to pos and current goes pos to neg" means.

Forgive my ignorance, but that apply to tubes cause it doesn't sound like it?

[JohnR]

In a vacuum tube, electrons flow from the cathode to the anode. With regard to velocity, I don't know, I was referring to wire

Actually, that's an interesting point though - the reason the cathode is heated is so the electrons get excited and leave (so to speak).

[werd]

Hi Werd,electrons as we know always go from neg. to pos.I'm trying like you to grasp some of this stuff at 53.I got these old red and orange paper back books on e-bay that were used in the 50's to train Navy guys as fast as possible.In issue #1 it is stated in the early days of electronics,the( conventional current) was from positive to negitive,but that was wrong,an electron current goes from neg. to pos.(Basic Electricity by Van Valkenburg...Vol.1).....Hey Werd,I'm lost a little bit too.I went to summer school for math,and Ohms law is looking like a Marine boot camp obsticle....let me know..Mark Korda

Hi

Yes this is what i mean. Except that electrons and current travel in opposite directions according to this EE i was listening to. Its just an interesting theory. Voltage travels in the updated electron flow neg to pos. And the current travels in the old Conventional flow direction and they meet where ever voltage drops. Unrelated I had an old physics teacher explain that the current was a dumptruck and the voltage was its load. They would go in the same direction and the dump truck would drop voltage at every load until empty... hehe.  The EE and my old physics teacher had two different takes on it.

I have no idea on this but i found it very interesting and i thought i would throw it out there.

[JohnR]

electrons and current travel in opposite directions according to this EE i was listening to. Its just an interesting theory.

It's not a theory, it's just how it works. 

[Speedskater]

The confusing part is text books! At one level they write about electricity (not electrons) flowing positive to negative yet at another level electricity flows negative to positive. Back in vacuum tube days the negative to positive flow made more sense because it was the same as electron flow in tubes. But now with solid state, electrons flow one way and holes flow the other.

[geezer]

Electric current exists wherever electric charges are in motion, whether the charges are positive or negative. The electric current is proportional to the product of the charge that is moving times the velocity of the motion. In some cases the current is carried by BOTH positive AND negative particles, as in a lightning strike or an ionic fluid, where there are both electrons and positive ions involved, as well in some solid state substances where negative electrons and positive 'holes' are involved.

In the following, bold symbols stand for vectors.

You need to know that, mathematically, electric current I is proportional to the charge that is moving, q, times its velocity V. The proton, e.g., has a charge that is traditionally indicated by the letter e. The charge on the electron is -e. So if protons are carrying the current, the current is given by I_p=KeV_p, where V_p is the velocity of the protons. (K is a positive constant whose magnitude depends on the units being used.)

Now suppose these protons are moving from a positive pole at point A to a negative pole at B, and simultaneously there are electrons moving (of course) from B to A, i.e, from negative to positive. Then the current carried by the electrons will be:
 I_e=K(-e)V_e. But this can be written as: I_e=K(e)[-V_e]. Now since V_e is opposite V_p, then we can see that -V_e is in the same direction as V_p. This shows how the current of electrons is in the same direction as the protons even though they are moving in opposite directions.

If you're not familiar with vectors, this might be confusing to you. To really understand what's going on mathematically, you have to have a certain amount of context, which you probably could get in many high school physics texts, if you have the stamina.

[ctviggen]

It's not a theory, it's just how it works. 

That's because they define current movement as movement of the "holes", in this case the positive charge.  One could easily define current movement as movement of the electrons.  It just means every sign would have to be reversed.

[ctviggen]

The confusing part is text books! At one level they write about electricity (not electrons) flowing positive to negative yet at another level electricity flows negative to positive. Back in vacuum tube days the negative to positive flow made more sense because it was the same as electron flow in tubes. But now with solid state, electrons flow one way and holes flow the other.

That's because when an electron moves from one atom to another, it leaves behind a positive charge, a "hole" on the first atom. 

[geezer]

That's because they define current movement as movement of the "holes", in this case the positive charge.  One could easily define current movement as movement of the electrons.  It just means every sign would have to be reversed.

That's true. Just as the charge on the electron could have been (but wasn't) defined as positive, which would make the proton charge negative. The definition is arbitrary. However the definitions that the world of physics, chemistry, etc., are what I used. The essential thing is to have everyone using the same definitions, otherwise communication becomes awfully difficult.

[jneutron]

Which way do electrons flow?  Do they go positive to negative or vise versa? I only ask this since i heard a very interesting theory that voltage goes "neg to pos and current goes pos to neg". And they are measureable where voltage drops. Interestiing theory from an EE that  picked this up in university.

Electrons flow from negative to positive.

However, in the world of electrical engineering, current is defined as going from positive to negative.  Back in the day, Ben Franklin defined the direction of current flow, but at the time the existence of the electron was not known.  Hey, he had a 50% chance of getting it right..

The right hand rule makes the assumption that "current" flows pos to neg, this is the standard engineering convention.

The left hand rule is used for the flow of electrons, this is the standard beam physics convention.

You've no idea the confusion this generates when explained to a roomful of high energy particle physicists..  So, don't be concerned that it seems confusing..it is..

Cheers, John

[AVnerdguy]

Yes, it can be confusing. In the repair world (I used to teach electronic equipment repair) we use electron flow which is electrons flow from negative to positive. And, it refers to a more positive potential - i.e. the devices can both be a positive voltage but it will flow from the least positive to the more positive - like a tube where the plate is at a higher positive potential.

Conventional flow as used in the old engineering days was that it flowed from positive to negative but the engineering schools have been getting away from that over the years and are teaching electron flow as well.

[geezer]

Electrons flow from negative to positive.

However, in the world of electrical engineering, current is defined as going from positive to negative.  Back in the day, Ben Franklin defined the direction of current flow, but at the time the existence of the electron was not known.  Hey, he had a 50% chance of getting it right..

The right hand rule makes the assumption that "current" flows pos to neg, this is the standard engineering convention.

The left hand rule is used for the flow of electrons, this is the standard beam physics convention.

You've no idea the confusion this generates when explained to a roomful of high energy particle physicists..  So, don't be concerned that it seems confusing..it is..

Cheers, John

Clearly, you've never been in a room full of high energy particle physicists.

[turkey]

Hi Werd,electrons as we know always go from neg. to pos.I'm trying like you to grasp some of this stuff at 53.I got these old red and orange paper back books on e-bay that were used in the 50's to train Navy guys as fast as possible.In issue #1 it is stated in the early days of electronics,the( conventional current) was from positive to negitive,but that was wrong,an electron current goes from neg. to pos.(Basic Electricity by Van Valkenburg...Vol.1).....Hey Werd,I'm lost a little bit too.I went to summer school for math,and Ohms law is looking like a Marine boot camp obsticle....let me know..Mark Korda

For anyone who's interested, try: http://www.tpub.com/neets/

[jneutron]

Clearly, you've never been in a room full of high energy particle physicists.

Really?  Why is it clear that I have not?

I was presenting magnetic conventions to 40 or so particle physicists, so that all the magnets I am responsible for connecting are wires correctly...900 of them.

When I defined how the magnets are powered to produce the correct fields, nobody complained..when I defined the magnetic fields for the bending of the beam, one third of the room raised their right hand, three fingers orthogonal...one third the left hand, and one third raised both.

The visual was so funny I almost peed my pants..

Cheers, John

[geezer]

Really?  Why is it clear that I have not?

I was presenting magnetic conventions to 40 or so particle physicists, so that all the magnets I am responsible for connecting are wires correctly...900 of them.

When I defined how the magnets are powered to produce the correct fields, nobody complained..when I defined the magnetic fields for the bending of the beam, one third of the room raised their right hand, three fingers orthogonal...one third the left hand, and one third raised both.

The visual was so funny I almost peed my pants..

Cheers, John

Well, I'm not sure what you mean by "particle physicist". What I mean is a theorist, or an experimentalist who plans experiments and sees that they are correctly carried out. To be able to do such, he/she has to have intimate knowledge of relativity, quantum mechanics, classical mechanics, thermodynamics, electrodynamics, the standard model, and more. And when I say "intimate knowledge", I don't mean just in qualitative terms; I mean being able to use the relevant equations (e.g., the Dirac equation, Schroedinger equation, etc.) and wrestle the necessary numbers out of them correctly. Most of them have taught these things.

Also, different people in the room probably were considering different issues. For example while one might have been working out the direction of the magnetic field from the direction of the current in the magnet windings, another might have already worked that out, and was determining the direction of the vector cross product of the magnetic field with the particle velocity to determine the direction of the force exerted.

Not having been in the room you refer to, I can't comment on specifics, but I have known hundreds of particle physicists, and I can assure you any one of them (as defined above) would think it hilarious that such an elementary issue should be considered confusing.

In the interest of full disclosure, I should say I am a particle physicist. (Or was; I'm now retired.)

Regard,

Geez

[blutto]

...the good news is I didn't pee my pants when I read that ...the bad news is I now have coffee all over my key-board and my screen...

...been in similar situations several times so that really resonated...another log on the departmental humour pile...thanks, that made my day...

Cheers

blutto

[jneutron]

Well, I'm not sure what you mean by "particle physicist".

Well, lets see.

definition of particle physicist...

1.  Experimentalist:  thinks up weird things to build like muon rings, antiproton decellerators (sp), stochastic cooling, electron lenses, antimatter confinement magnets..  Discusses with me the absolute maximum capabilities of Niobium Ti, Niobium Tin, and HTS that I can use to fabricate magnets, then writes a specification that requires 1.5 times what I told him is possible with respect to short sample, and at least 2 times the field quality I 've been able to achieve.  The lesson learned when dealing with an experimentalist:  Tell him (her) that you can only do 50% of what you actually can do.  Then, you may actually be able to make what they need..

2.  Theorist:  again, thinks up weird things like muon rings and the such.  But I have no clue what they are doing anyway..when I ask them to explain, I regret it...bartender...more drinks..  But when we meet at happy hour, they are actually human..go figure.

3.  Subset, unknown pedigree..co-worker:  Designs superconducting magnets, measures field quality of everything...Has NO textbooks in his office, especially anything on e/m theory...  When asked why, the answer:  he starts with maxwell's equations and derives everything he needs..that way he knows it's correct..I can only trust him...The last derivation he did was 50 pages long..he asked me to review it, but halfway down the first page he started using symbols I never saw before..

4.  Subset, also unknown pedigree...also questionable as to "high energy", as I'm not sure if a 3 Gev e-beam light source (third generation) is high enough to qualify as "high energy"..Ya gots your lattice guys, ya gots your wiggler guys, ya gots your undulator guys, and ya gots your rad guys.

All I knows is..they tell me that historically speaking, 50% of the magnets in all the light sources built in the last decade or two were connected backwards..I think it has something to do with room temperature operation.  That's not what happened in the 4.5 kelvin thingy I was a small part of 14 years ago.. that is simply because it costs way too much to "de-weld" the cryostats to fix dipole, quad, or sextupole circuits..the bellows are shall we say, big time PITA's?

Not having been in the room you refer to, I can't comment on specifics, but I have known hundreds of particle physicists, and I can assure you any one of them (as defined above) would think it hilarious that such an elementary issue should be considered confusing.

When it happened, I was also confused, as I'd never considered the fact that the beam current is reversed because it's an e-beam.  I just went with Tonagi's conventions, electrons travelling in the same direction attract..then went from there.  Course, I had to trust the lattice guys with focussing quads and sextupoles, they are not intuitivly obvious to me..

In the interest of full disclosure, I should say I am a particle physicist. (Or was; I'm now retired.)

Well don't worry..I won't hold that against you...

Do any PAC conferences?

Cheers, John

PS...I'm sorry, I gotta call you on one specific thing.

Retired particle physicist???  Yah, right..  There is no such thing..at least, not on the east coast..