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Topic: Which direction does current flow? (Read 8538 times) previous topic - next topic


Jun 07, 2018, 03:44 am Last Edit: Jun 07, 2018, 03:51 am by MrMageeyee
I am trying to map out a circuit, and I don't know if electrons** flow from ground to 5V or vice versa?  Thanks!


Jun 07, 2018, 03:50 am Last Edit: Jun 07, 2018, 03:54 am by terryking228

That is actually a good question and discussed a lot. In the 1880's especially.  

What is actually flowing is ELECTRONS, which are little negative charged particles. They are attracted by positive voltages. So ELECTRONS flow from "Ground" to "VCC" on an Arduino. This is "Electron Flow"..

BUT the OldSkool "Conventional Current Flow" assumes current (whatever THAT is) flows from Plus to Minus.

WikiPedia "Electric Current" 

The ELECTRONS really don't care, but get a charge out of all the arguments...
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Thank you! That was exactly what I was asking!


Oh NO! Hole flow, electron flow, it's maddening I tell ya!

I was taught electron flow, so current is from ground to positive potential.
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Jun 07, 2018, 04:23 am Last Edit: Jun 07, 2018, 04:23 am by DrAzzy
It's worth noting that you really don't need to care which direction electrons are actually flowing (and engineers, in practice, rarely talk about that, just about positive and negative voltages and currents.

By convention, current flow is from positive to negative (convention set before we knew what electrons were)
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Jun 07, 2018, 04:51 am Last Edit: Jun 07, 2018, 05:10 am by Southpark
I agree with DrAzzy. As long as you assign polarity symbols for components (where necessary).... which means voltage polarity symbols, and current direction (arrow) symbols, and write down values of voltages (eg. +5V or -5V) and currents (eg. 2A or -2A), then we can just focus on analysing the circuit.... such as figuring out whatever we need to figure out.... like other voltages and currents or power within the circuit.



First, I took electronics in high school and I learned that electrons flow from negative to positive.

Then I took electronics in college and learned that current flows from positive to negative.

Then I took college physics and I learned that current (electrons) flows from negative to positive.

...Finally, I understood that "conventional current" is a concept, and I understood that in the engineering world you've got to go-along with the convention.


How about AC ? - LOL
For AC circuits, the same deal applies. Still got to use a circuit sign convention..... eg. passive sign convention, for basic circuit analysis and design.


...Finally, I understood that "conventional current" is a concept, and I understood that in the engineering world you've got to go-along with the convention.
Having a general agreement (everyone following some sign/compatible convention) allows for consistency in results I guess.

For physics, I'm guessing that they could easily have said that electrons have 'positive' change. Definitions is what it is.

Somebody needed to say --- we got to make a choice..... let's go with this/it.

It's sort of name for right-hand left-hand..... we could easily have chosen the reverse of it.


Jun 07, 2018, 08:50 am Last Edit: Jun 07, 2018, 08:51 am by ReverseEMF
Not sure if this was said -- didn't read all of the comments, so:

As others have said, there is the Electron Flow convention, AND the Conventional Current convention.  The bottom line, and important detail is: pick a convention and stick with it throughout the circuit.

I usually choose Conventional Current, because, then all the arrows make sense [on diodes, transistors, SCRs, etc.] ;)

In electronics, it usually doesn't matter which direction the current is flowing.  In physics you will probably care about that, but when designing circuits, just pick a convention and stick with it.
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Electrons don't really flow. They just jump to the next atom, which displaces another electron, etc., etc. The holes flow, but then holes aren't really anything.
What, I need to say something else too?


Jun 07, 2018, 10:23 am Last Edit: Jun 07, 2018, 10:24 am by Southpark
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.


And for added fun, while the current moves at light speed, the electrons (and holes) move in the tune of millimeters or centimeters an hour... if it's DC... in case of AC they're just moving back and forth, not going anywhere really!
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Jun 07, 2018, 12:19 pm Last Edit: Jun 07, 2018, 12:20 pm by MarkT
Electrons don't really flow. They just jump to the next atom, which displaces another electron, etc., etc. The holes flow, but then holes aren't really anything.
Depends what they flow in.

For a vacuum, electrons are in free fall but strongly dominated by any electric field (much much stronger
than gravity),
for metals and conduction band in semiconductors electrons flow - they are not bound to atoms.
Holes in semiconductors are more complex, since they emerge from bound (valence) electrons hopping
from atom to atom.  Holes are less mobile than electrons, and this I think is the principal cause (but
I may be wrong, solid state physics is not trivial!)

Unbound electrons in metals are actually moving around at random at _very_ high speeds(*) all the time, the
actual macroscopic current is a slow drift superimposed upon that.  Due to the electric field all the rapid
random electron motion is correlated and cancels out on the large scale, so we almost never have to worry
about this (fortunately).  These electrons occasionally scatter off some of the atoms (which is the cause of electrical resistance)

(*) copper has a Fermi velocity of around 1600 km/s, typical drift velocities in copper wires are measured
in mm/s, 9 orders of magnitude smaller.
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