Which direction does current flow?

Using Arduino General Electronics
#33

ReverseEMF: I think you're confusing current flow in a conductor with current flow in a semiconductor.

  • Conductor: Movement of free electrons [a property of metals].
  • Semiconductor: More like what you're describing [a property of specially doped semimetals or more exotic alloys].

Yes. You are absolutely correct, I am speaking of a semiconductor. Of course, nearly every (non-super)conductor has some semiconductor characteristic. "Free" electrons are not perfectly mobile in a conductance band. For a conductance band is not a band at all, but closely overlapping high energy orbitals in a close packed array of atoms. The electrons need to jockey for position, because, although there are a lot of states, Pauli still applies. In a piece of wire the mass of the electrons crawls along many thousand times slower than the movement of the charge, aka the current.

It's within this jumble of buzzing electrons that the holes exist - they are unoccupied orbitals.

#34

Chris is right about that. Eg.... a parallel plate capacitor. During the charging and discharging stages, the electrons don't move across the 'gap' from one side of the plate to the other when a voltage source is applied across the two plates.

There is no electron movement across the plates of a capacitor. When an AC signal is impressed across the capacitor, there is the flow of electrical energy. Flow of electrical energy involves the flow of current. This is Maxwell who introduced the concept of displacement current which flows across the capacitor plates due to change in electric flux to enable energy flow. (it = ic + id = conduction current due to carrier + displacement current due to electric flux change)

#35

Grumpy_Mike: The hole.

I think he was asking for a definition of what "moving" really means rather than for the thing that is moving.

#36

All this talk of holes or absences of electrons moving reminds me of a nice Terry Pratchett quote:

Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first, and is waiting for it.

:)

#37

I love it when we take a subject like this and run with it...

I see it like the small trees I just planted in my yard.

The holes we are talking about are an atom in a lattice that has the LACK of one electron.

If there are 3 holes in a row, and the first one acquires an electron, there are 2 'holes'.

If the electron moves from hole 1 to hole 2, the hole 1 reappears.

If I put a tree temporarily in my first hole, there are two holes left.

If I move the tree to the center hole, there are two holes left.

So I can propagate holes. Trees can drift in one direction, and holes (the LACK of a tree) can propagate in the other direction.

OK, enough... I gotta go water those trees.

#38

Grumpy_Mike: The hole.

I still maintain that the hole doesn't "move". Holes merely appear and disappear--as electrons occupy/vacate orbitals. Movement is a "useful delusion", in the same way cinema is. The appearance of movement on the screen is a phantom created by the mind. And, in fact, the so called movement of holes isn't even seen. That's why I used the word "delusion" in association with hole movement, and illusion in terms of movie *movement. *

In fact, isn't it true that there isn't, even, a physical hole--as in some stationary pit surrounded by boundary defining electrons? I mean, in reality, it's just one less probability cloud, around the nucleus of an atom, right? So, to call that a hole, is even more delusional, right? And by delusional, I mean, a model, and not an actual thing. A useful delusion.

So, hole, is a model for a missing electron cloud -- which doesn't really resemble a hole. And, any movement of this phantom entity, is only conceptional. In an electric field, they do seem to move, but not really -- but, it's useful to think of it that way.

And, consider this: locking yourself into a way of thinking, based on an accepted model, makes it difficult to advance the field. Einstein was able to discard models and think beyond them. Because he was able to think beyond Newtonian Physics, he knocked Physics on its ear. The history of the conceptualization of the atom is another good example. If physicists had decided that the plumb pudding model was the end-all-be-all, science would not have found its way to orbitals and the to the current, very strange, model of the atom -- and it's still a model!

But, I'm not a Physicist. :P

#39

terryking228: So I can propagate holes. Trees can drift in one direction, and holes (the LACK of a tree) can propagate in the other direction.

The holes themselves are still pretty firmly in place... it's just that one appears when you take out the tree, and it disappears when the tree is placed in one. The location of where a hole is moves. The hole itself doesn't.

#40

wvmarle: The location of where a hole is moves.

How do you know it's the same hole?

#41

ReverseEMF: How do you know it's the same hole?

It just has to be as it's not the same location, right? Unless it's a black hole, but then that's most likely because someone dropped a can of paint.

Aaargh!

#42

The absence of the electron in the covalent bond is represented by a small circle, and such an incomplete covalent bond is called hole. The importance of the hole is that it may serve as a carrier of electricity comparable in effectiveness to the free electron. The mechanism by which a hole contributes to the conductivity is qualitatively as follows: When a bond is incomplete so that a hole exists, it is relatively easy for a valence electron in a neighboring atom to leave its covalent bond to fill this hole. An electron moving from a bond to fill a hole leaves a hole inits initial position. Hence the hole effectively moves in the direction opposite to that of electron. This hole, in its new position, may now be filled by an electron from another covalent bond, and the hole will correspondingly move one more step in the direction opposite to the motion of the electron.

#43

wvmarle:
It just has to be as it’s not the same location, right? Unless it’s a black hole, but then that’s most likely because someone dropped a can of paint.

Aaargh!

What if electrons leapfrog atoms, and populate holes more than one atom away [leaving the adjacent hole–the one expected to catch that wayward electron–to be filled by another leapfrogging electron]? Or, maybe they don’t always travel along the same “level” but can, also, jockey for positions on different three-dimensional levels. Is it really known if electrons always leap to holes that are exactly adjacent? How do you maintain the identities of holes that leap around in such an unpredictable manner? If you point to an adjacent hole and say you know it’s previous location, you would be wrong some [or even most] of the time.

And, what if, in a Universe where this is true, understanding this subtality of movement, and how to control it, leads to the next fulfillment of Moore’s Law?

Just an example of how getting too ensconced in a model can cloud creative thinking–and ultimately: progress.

#44

GolamMostafa: The absence of the electron in the covalent bond is represented by a small circle, and such an incomplete covalent bond is called hole. The importance of the hole is that it may serve as a carrier of electricity comparable in effectiveness to the free electron. The mechanism by which a hole contributes to the conductivity is qualitatively as follows: When a bond is incomplete so that a hole exists, it is relatively easy for a valence electron in a neighboring atom to leave its covalent bond to fill this hole. An electron moving from a bond to fill a hole leaves a hole inits initial position. Hence the hole effectively moves in the direction opposite to that of electron. This hole, in its new position, may now be filled by an electron from another covalent bond, and the hole will correspondingly move one more step in the direction opposite to the motion of the electron.

That's a nice description of the currently accepted model.

#45

Then there's also the problem of an electron moving/leapfrogging/whatever. According to quantum physics, what we call "the location of the electron" is just the place where (it is most likely to)(most of it can) be found, but in reality it supposedly can be just about anywhere in the universe, and that preferably at the same time. So even the "moving of an electron" is probably an incorrect description.

#46

A hole has a mass you can weigh it. A hole can move in a substrate. It has velocity. A hole can collide with other holes and bounce off them.

All these “missing” electron stories are just that, a convenience fiction for those who don’t want to go too deep into the theory. Holes are real.

#47

I see a bunch of people who really got deep into this subject. I never learned too much about it, but I do know this- out of holes, electrons, and current-current is the one that will really get your attention

#48

tinman13kup: I see a bunch of people who really got deep into this subject. I never learned too much about it, but I do know this- out of holes, electrons, and current-current is the one that will really get your attention

I think the main thing is just to consider (as these scientists appear to be suggesting) .... is to think of the universe as some kind of system .... some matrix, and for some unknown reason (simply unknown), there are building blocks.... or more like building 'forces'. So some combinations of these building 'forces' get together (somehow) to form things like fields, protons, quarks, sparks, neutrinos, electrons, photons, atoms, etc. The atoms and molecules appear to be what we 'define' as solid. All these physical 'stuff' is defined by humans --- we 'sense' them, or 'measure' them, or predict them ....and we define them.

In this universe, people don't even know what the origins are..... of electrons, holes, fields, etc. They just know how to define and measure these 'quantities'/'entities' that they see or sense, and know how to make use of them ----- ie. do things with them if they can.

So, as long as something like 'holes' is defined, then just treat holes as yet another physics defined 'thing'. And just use current as whatever it is defined to be by physicists....and use current as it is shown in circuit theory (ie. adopt a convention, and go for it).

As for OP's question of which direction does current flow..... if just focusing on basic circuit theory, just go with most circuit theory text books and use 'conventional' current flow ----- and use a sign convention for voltage, current and power .... aka 'passive sign convention'. You would only get into the hole and electron discussion when entering the physics area.

#49

Oh, I know our hobby end of electronics doesn't even scratch the surface of the big picture when it comes to physics. I just have a suspicion the Grumpy_Mike used to be known as Happy_Mike before college.

#50

when it comes to physics. I just have a suspicion the Grumpy_Mike used to be known as Happy_Mike before college.

I was only temporarily a Uconn Physics Major (1958) , but I was only Grumpy because they wouldn't Frickin' let me TOUCH anything. "When you are a Senior, you can do a Project".. Grr.... So I dropped out...

NOW: Every entering Engineering and Computer Science student goes to the Bookstore and BUYS MY KIT! Barnes and Noble just ordered 700 for the Uconn bookstore. OMG, it took 60 years to get my Revenge!

I am so happy that times have changed and it's understood that early hands-on experience is vital to getting kids really involved with things that are INVISIBLE. Like my kit says, "UH-OH! Electricity is INVISIBLE"..

Mike, please explain (Yeah, I know... I didn't major in Physics..) how a "Hole" has measureable weight. Is it the mass of a (for example Silicon) atom, minus the mass of an electron?? Hmmm....

#51

Grumpy_Mike: A hole has a mass you can weigh it. A hole can move in a substrate. It has velocity. A hole can collide with other holes and bounce off them.

All these “missing” electron stories are just that, a convenience fiction for those who don’t want to go too deep into the theory. Holes are real.

Science is just another mythology. Probably a better **informed mythology than most, but when you get down to brass tacks, no one really knows what it all really is. Any "scientist" who thinks otherwise, is living, and thinking in a deluded state.

#52

no one really knows what it all really is.

A statement like this always makes me want to ask what it would mean or what it would take to really know what it all really is. To make a statement like that requires that you know. So by all means, tell us.