AC vs DC and the flow of electrons

  • Thread starter WarrickF
  • Start date
Hi All,

I'm trying to visualize the flow of electrons in an AC circuit.

DC is pretty simple as I can imagine the electron moving from point A to B.

AC on the other hand confuses me. If there's a constant switch of polarity one would imagine that the electron would move forward as the wave becomes more positive .. but then when the polarity switches surly the electron would end up moving back to the location is started from?

The above description just seems crazy as the electrons would simply "slosh" back and forth never going anywhere. Clearly I'm missing something :) ... could someone please explain or ref. an article that explains this to the mortal.

Thanks
Warrick
 
423
1
Hi WarrickF,

Why is it odd to you that the electrons slosh back and forth never going anywhere?

This analogy may help:

When you cut a wood using a saw, your saw moves back and forth but it cuts the wood finally. The same way electrons give power to a resistor by their back and forth motion.

When a wood is cut by a machine saw, the saw moves in one direction on the wood and cuts more effectively as DC current give more power to the same resistor compared with the AC current whose peak current is equal to the DC current.
 
We know that electron flows at a very high velocity that getting a comple visulaization would be hard. But just curious to know if this being explained or related to wave-particle duality of the electron in quantum physics.
 
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This is drift velocity which usually very small.
 
So I should clarify that i'm not asking this to try and understand any deeper concepts like wave duality etc, simply so that I have a better understanding of the basics.

I guess in my mind I still don't feel like I'm seeing the whole picture. Let's take an experiment as an example.

9V DC battery -> (9V - 120V Transformer) -> 120V Light Bulb

If I introduce pulsating DC current to the 9V end of the transformed, I'll get 120V AC on the other end. Now if this "sloshing" effect were true one would imagine that the 120V side would someone become saturated with electrons.

Sorry, I realize that my thought is not really focused here I'm thinking out loud.

Thanks
Warrick
 

HallsofIvy

Science Advisor
41,625
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So I should clarify that i'm not asking this to try and understand any deeper concepts like wave duality etc, simply so that I have a better understanding of the basics.

I guess in my mind I still don't feel like I'm seeing the whole picture. Let's take an experiment as an example.

9V DC battery -> (9V - 120V Transformer) -> 120V Light Bulb

If I introduce pulsating DC current to the 9V end of the transformed, I'll get 120V AC on the other end. Now if this "sloshing" effect were true one would imagine that the 120V side would someone become saturated with electrons.
I can't imagine why you would think that. The whole point of "sloshing", as you put it, is that the electrons to "back and forth". There is no accumulation or saturation with electrons anywhere.

Sorry, I realize that my thought is not really focused here I'm thinking out loud.

Thanks
Warrick
 
I'm asking not telling. But if current is developed by the moving of electrons, does it matter wheater they move in a line or "shosh around"?
 

nsaspook

Science Advisor
878
1,084
Hi All,

I'm trying to visualize the flow of electrons in an AC circuit.

DC is pretty simple as I can imagine the electron moving from point A to B.

AC on the other hand confuses me. If there's a constant switch of polarity one would imagine that the electron would move forward as the wave becomes more positive .. but then when the polarity switches surly the electron would end up moving back to the location is started from?

The above description just seems crazy as the electrons would simply "slosh" back and forth never going anywhere. Clearly I'm missing something :) ... could someone please explain or ref. an article that explains this to the mortal.

Thanks
Warrick
Good, You now see that the actual electron net movement direction is not the same as the energy flow direction.

http://www.eskimo.com/~billb/miscon/eleca.html

In AC electric circuits the charges wiggle back and forth, but the energy moves continuously forward. This is analogous to the way that sound waves move continuously forward through the air, while the air itself wiggles back and forth. But if we teach our kids that "electricity" is made of electrons, and "electricity" is also energy, then we make a serious error. We unwittingly teach them that the electricity in wires sits in one spot and wiggles, but at the same time the electricity moves forward at nearly the speed of light. Garbage! It's like saying that sound and air are the same thing. And the error is directly traceable to the bogus "electricity" concept.
 

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