Author Topic: This electons flowing rubbish  (Read 7049 times)

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Offline Terry BitesTopic starter

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This electons flowing rubbish
« on: March 01, 2021, 02:24:14 pm »
Why do people just keep on promoting bad science?

Electrons do not flow in conductors or semiconductors or anything else when a current is flowing. Yeah Yeah drift current... diffusion current... blah.
Charge is transported around the current path under the influence of the applied voltage.

Let's stamp out the BS in EE!


 

Offline TimFox

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Re: This electons flowing rubbish
« Reply #1 on: March 01, 2021, 02:56:44 pm »
There are exceptions to your absolute statement.  For example, electrons do flow from a hot cathode to the anode under "saturated" condition (not limited by space charge), with the resulting shot noise in the current in the rest of the circuit.  (Space charge modifies the equations, but the flow to the anode is still a host of electrons at a reasonable velocity.)
Usually in the first chapter about "current" in an undergraduate physics textbook on electromagnetism there will be a list of examples of different physical situations where there is current flow, including the vacuum diode above.
« Last Edit: March 01, 2021, 03:23:35 pm by TimFox »
 

Offline T3sl4co1l

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Re: This electons flowing rubbish
« Reply #2 on: March 01, 2021, 03:27:57 pm »
I suppose it's tricky.  A hydraulic analogy is quite productive.  There, too, the drift and particle velocities are widely disparate; perhaps one should be careful to emphasize the relevance of the speed of sound (mean velocity of molecules) in that case, and show the analogy with electron drift.

But it's also hard to motivate that; you can't splash some water around and say that it happened at the speed of sound, no, it's much too fast to see.  It's easily illustrated with resonators and frequency or step response, but those require much more knowledge (dynamics, wave mechanics) to understand.  Worst of all, electron waves flow at the speed of light in the medium, not at the thermal velocity, so the analogy again breaks down, in a different way.

And neither case seems to be good preparation for the student, for the truth that alternating current flows largely in the space between conductors, rather than in them (in the bulk) as such.

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Offline IanB

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Re: This electons flowing rubbish
« Reply #3 on: March 01, 2021, 03:40:48 pm »
Charge is transported around the current path under the influence of the applied voltage.

So I'm slightly curious. How is charge transported around the current path without mobile charge carriers?
 

Offline TimFox

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Re: This electons flowing rubbish
« Reply #4 on: March 01, 2021, 03:46:27 pm »
In simplistic terms, I like to think of current flow through a normal solid conductor as a slight tendency of a zillion electrons to move to the right under the influence of the potential difference from left to right, superimposed on their random thermal motion that exists even without applied voltage.
 

Offline bdunham7

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Re: This electons flowing rubbish
« Reply #5 on: March 01, 2021, 04:06:43 pm »
Why do people just keep on promoting bad science?

No model is perfect, but that doesn't mean we throw them out when science reveals a new refinement or wrinkle.  Your assertion is along the lines of those who claim Newton was wrong because F=MA is 'bad science' just because it appears to not be exactly true in some regards.

For DC current, the average velocity of the electrons in a conductor would be easily calculated if you know the number of electrons moving (the current), the length of the wire and the number of the electrons in the wire.  The only tricky part is that this gives you the average velocity of all the electrons, not just the ones that actually move.  So now you have to define your terms and see if you want to just count the ones that actually move and then you have to see if you can determine that number for your material.

https://en.wikipedia.org/wiki/Drude_model#Drude_response_in_real_materials

Like any model, especially those predating quantum physics and relativity, Drude has its limits.  That doesn't make it 'bad science'.
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Offline Alex Eisenhut

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Re: This electons flowing rubbish
« Reply #6 on: March 01, 2021, 04:22:12 pm »
How do these work?







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Offline penfold

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Re: This electons flowing rubbish
« Reply #7 on: March 01, 2021, 04:35:44 pm »
Would a change in terminology make it better? We could have "a flow of current caused by a floundering of electrons"
 

Offline JohnnyMalaria

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Re: This electons flowing rubbish
« Reply #8 on: March 01, 2021, 06:09:59 pm »
Why do people just keep on promoting bad science?

Electrons do not flow in conductors or semiconductors or anything else when a current is flowing. Yeah Yeah drift current... diffusion current... blah.
Charge is transported around the current path under the influence of the applied voltage.

Let's stamp out the BS in EE!

It's not bad science. It's an appropriate model to explain the observed phenomena and allow us to exploit those phenomena. Unless you taught everything from the perspective of Unified Field Theory, then it would all be bad science, too.

Is teaching Newton's law of gravity bad science?
 

Offline Alex Eisenhut

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Re: This electons flowing rubbish
« Reply #9 on: March 01, 2021, 06:35:24 pm »
Oh and what are "electons"?
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Offline RoGeorge

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Re: This electons flowing rubbish
« Reply #10 on: March 01, 2021, 07:06:18 pm »
Why do people just keep on promoting bad science?
I don't know, but that's exactly what you are doing right now.  You are promoting bad science.

Electrons do not flow in conductors or semiconductors or anything else when a current is flowing.
Electrons do flow.  If you are upset for why they do not flow in a straight line, then you shouldn't.  Wrong expectation.  Flow is not necessarily in straight line, in fact it's almost never in a straight line.

Does water flow?  Water molecules also wiggle around while flowing.
Does air flow?  Gas molecules have an even larger Brownian motion.

Looks like it's correct to say electrons flow, too, thought the most widespread expression is "a flow of electrons".

Charge is transported around the current path under the influence of the applied voltage.
Could be like that, but not necessarily.

Charges can be moved by other means than applying a voltage.  For example, you can put charges on a piece of plastic then mechanically move the plastic band, and you'll have a current flow without applying any voltage.




As a generic advice, when the whole world seems wrong yet you seem right, usually it means you misunderstood something, or you are missing something.  Don't use emotional words like "rubbish", "blah" or "bullshit", don't be judgemental and don't act superior calling for the wrong action "let's stamp out".   :--

Better, explain what contradiction you noticed, then ask "what am I missing?"   :-+

Offline Gyro

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Re: This electons flowing rubbish
« Reply #11 on: March 01, 2021, 07:48:11 pm »
How do these work?

Ah, those are Cathode Rays  ;)
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Offline Cyberdragon

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Re: This electons flowing rubbish
« Reply #12 on: March 01, 2021, 09:00:01 pm »
How do these work?

Ah, those are Cathode Rays  ;)

You confuse rays with beams, D! Minus! I'd give you an F, but that would mean seeing you in summer school. ;D
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Offline JohnnyMalaria

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Re: This electons flowing rubbish
« Reply #13 on: March 01, 2021, 09:14:43 pm »
Time for an educational intervention:


 
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Offline Sal Ammoniac

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Re: This electons flowing rubbish
« Reply #14 on: March 01, 2021, 10:57:56 pm »
Charge is transported around the current path under the influence of the applied voltage.

So I'm slightly curious. How is charge transported around the current path without mobile charge carriers?

The same way momentum is transported in one of these:

"That's not even wrong" -- Wolfgang Pauli
 

Online Brumby

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Re: This electons flowing rubbish
« Reply #15 on: March 02, 2021, 12:11:45 am »
Why do people just keep on promoting bad science?

Electrons do not flow in conductors or semiconductors or anything else when a current is flowing. Yeah Yeah drift current... diffusion current... blah.
Charge is transported around the current path under the influence of the applied voltage.
:palm:

Quote
Let's stamp out the BS in EE!
You can leave whenever you like.
 
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Offline JohnnyMalaria

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Re: This electons flowing rubbish
« Reply #16 on: March 02, 2021, 12:17:45 am »
Why do people just keep on promoting bad science?

Electrons do not flow in conductors or semiconductors or anything else when a current is flowing. Yeah Yeah drift current... diffusion current... blah.
Charge is transported around the current path under the influence of the applied voltage.

Let's stamp out the BS in EE!

Um, what about situations where the movement of electrons (or other charged particles) generates the voltage???
 
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Offline IanB

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Re: This electons flowing rubbish
« Reply #17 on: March 02, 2021, 03:25:18 am »
The same way momentum is transported in one of these:



That's AC, not DC. Try to make Newton's cradle work in only one direction without a net movement of the balls through space.
 

Offline thermistor-guy

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Re: This electons flowing rubbish
« Reply #18 on: March 02, 2021, 04:57:18 am »
I guess the OP's point is that electron flow in circuits is rarely ballistic; in most cases, "electron flow" should be read as "net electron flow".
Yes, ok. EEs know that.

...
Charge is transported around the current path under the influence of the applied voltage.
...

Not always. One example: a crystal radio set. Entirely passive, no voltage is applied to the circuit, rather a travelling electromagnetic field

Another example: solar cell with load. No voltage is applied to the circuit, just a travelling electromagnetic field at optical frequencies.

Other examples : thermocouples and thermopiles generating an electrical current due to a temperature difference.

Energizing a circuit does not always mean applying a voltage to it. There are other sources of energy. EEs know that. Hobbyists know that.
 

Offline Cyberdragon

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Re: This electons flowing rubbish
« Reply #19 on: March 02, 2021, 06:37:06 am »
Why do people just keep on promoting bad science?

Electrons do not flow in conductors or semiconductors or anything else when a current is flowing. Yeah Yeah drift current... diffusion current... blah.
Charge is transported around the current path under the influence of the applied voltage.

Let's stamp out the BS in EE!

Um, what about situations where the movement of electrons (or other charged particles) generates the voltage???

What about superconductors? 8)

*drops mic* *leaves*
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Offline jonovid

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Re: This electons flowing rubbish
« Reply #20 on: March 02, 2021, 07:09:31 am »
I have the faith to believe in what my eye's can not see. and the test equipment to prove it to be true.  8)
Hobbyist with a basic knowledge of electronics
 

Online Berni

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Re: This electons flowing rubbish
« Reply #21 on: March 02, 2021, 08:13:49 am »
So by this logic i can no longer say that "water is flowing along my pipe" because the water molecules are actually whizzing around wildly in all directions trough brownian motion but on average they end up going slightly more towards one direction, so that on average the water ends up moving forwards trough the pipe. So from now on i should say that "water is diffusing under the influence of unequal pressure caused by statistical collisions trough varying proximity trough the cavity of my pipe"

It is perfectly acceptable to simplify a concept down to what matters for the use case. If you are a physicist putting together some physics experiment involving charged particles then yes you would care about it. If you are an electronics engineer designing a transistor amplifier circuit you just don't give a toss about the fine details of what electrons are doing, all you care is the current flowing trough your components. Those currents also create magnetic fields around your circuit that can induce other currents, but you know your circuit is only working with 10KHz so you also don't give a toss about those because even tho the effect is there, it is too tiny to actually affect anything.

Its not that engineers say "these weird hand wavey mumbo jumno things don't exist, we just have current flowing trough a wire" they actually say "These fine details of what happens don't really matter in my particular case since it doesn't affect the operation of my circuit, so i can safely simplify it down or ignore it without any adverse effects, great so i can just slap on ohms law and have my circuit finished by the end of the shift"
 

Offline Terry BitesTopic starter

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Re: This electons flowing rubbish
« Reply #22 on: March 02, 2021, 01:28:58 pm »
Thinking of the electron as a particle is another poor analogy. It's a particular disturbance in a system of fields.
Is your anode getting heavier?
 

Offline tszaboo

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Re: This electons flowing rubbish
« Reply #23 on: March 02, 2021, 01:49:45 pm »
It's just terminology. If everyone knows what "current" means, and its not a river, but a wire, what's the point of changing it? People dont confuse electronics calculations with hydrodynamics. Probably because hydrodynamics is more complicated.
And then there are electron holes, technical current, condenser microphone ( I guess to turn steam of sound into electrons), and so on. Do you also want 14 year old students to understand quantum physics, before they draw the circuit with the battery-switch-lamp? How about explaining how this current is transformed into heat, that is then turned into light?
 

Offline madires

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Re: This electons flowing rubbish
« Reply #24 on: March 02, 2021, 01:53:44 pm »
Would a change in terminology make it better? We could have "a flow of current caused by a floundering of electrons"

ADHD electrons? ;D
 


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