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Topic: Which direction does current flow? (Read 1 time) previous topic - next topic

ReverseEMF

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Grumpy_Mike


ChrisTenone

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.

.sig

GolamMostafa

#33
Jun 08, 2018, 11:09 am Last Edit: Jun 08, 2018, 06:15 pm by GolamMostafa
Quote
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)

wvmarle

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

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

terryking228

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.
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
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ReverseEMF

#37
Jun 08, 2018, 05:07 pm Last Edit: Jun 08, 2018, 05:19 pm by ReverseEMF
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
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wvmarle

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.
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ReverseEMF

The location of where a hole is moves.
How do you know it's the same hole?
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wvmarle

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!
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

GolamMostafa

Quote
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.

ReverseEMF

#42
Jun 08, 2018, 06:37 pm Last Edit: Jun 08, 2018, 07:11 pm by ReverseEMF
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.
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ReverseEMF

#43
Jun 08, 2018, 06:42 pm Last Edit: Jun 08, 2018, 06:42 pm by ReverseEMF
Quote from: GolamMostafa date=1528410370
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.
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wvmarle

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.
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