Electron flows

Discussion in 'General Electronics Chat' started by anthonylauly, Jan 12, 2017.

1. anthonylauly Thread Starter New Member

Jan 7, 2017
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Hi, I would like to know if the electron flows from the negative or the positive side of the battery, and can I prove that with a simple circuit ?

2. WBahn Moderator

Mar 31, 2012
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Yes, in most circuits electrons flow from a more negative potential to a more positive potential. This can be demonstrated pretty conclusively with many tube-based circuits. With solid state circuits it is much more difficult because the most phenomena can be quite adequately explained by either negative charge carriers flowing from negative to positive or positive charge carriers flowing from positive to negative. However, there are some phenomena for which this is not the case -- one example is the Hall effect. So an experiment based on this phenomena can prove, at least in that device, what the polarity of the actual charge carriers is.

3. crutschow Expert

Mar 14, 2008
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Probably the easiest way is with a vacuum tube.
This can tell us not only the direction of electron flow in a battery but also the charge polarity of an electron.

Current will only flow in one direction in a vacuum tube diode.
That is from the hot filament cathode to the cold plate, and only when the plate is connected to the positive side of the battery and the cathode is connected to the negative side.
Since we know that opposite charges attract, this means that the positive plate must be attracting the charged electrons boiling off the hot cathode and the electrons thus must have a negative charge.
The also means the electrons are flowing from the negative to the positive side of the battery.

4. crutschow Expert

Mar 14, 2008
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Most?
Is there an exception to that?

5. WBahn Moderator

Mar 31, 2012
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Sure, there are circuits in which positively charged particles travel from a high potential to a lower potential, at least in portions of the circuit. As an example, consider ion beams.

ErnieM likes this.

Dec 27, 2016
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7. Elektrishun Member

Dec 27, 2016
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Does anything really flow when it comes to electrons/current? I read one description that suggested it's a bunch of vibrating particles that don't travel anywhere.

8. WBahn Moderator

Mar 31, 2012
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Keep in mind that the TS isn't asking about the age old electron-flow vs. conventional flow debate (which is what I expected the thread to be about, too), but rather is it possible to prove that, in non-special case (for lack of a better description) electric circuits is it possible -- and how might you go about it -- to prove that the charge carriers are, in fact, negatively charged and actually move from negative to positive.

9. WBahn Moderator

Mar 31, 2012
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In AC circuits with no DC component that is largely true, but even then it is a valid question whether the vibrating particles are positive charged or negatively charged. If there is a DC component then there is a net flow of charge carriers, though the velocity is generally quite low. But in many situations that is not the case. Again, vacuum tubes and charged particle beams are obvious examples.

10. crutschow Expert

Mar 14, 2008
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Yes, the velocity of an electron in a wire for typical current levels in pretty slow.
For example, for 5Adc flowing in a copper wire with a cross section of 0.5mm², the average velocity of an electron is about 0.735mm/s or 44mm/min.

For 5Aac in that same wire at 60Hz the electron would move about 6μm in a half-cycle, thus the electron does essentially vibrate in place with AC current in a wire.
(Makes you realize how many free electrons there are in a small piece of copper wire.)