Which direction does current flow?

I am trying to map out a circuit, and I don’t know if electrons** flow from ground to 5V or vice versa? Thanks!

dc_motor_connections.jpg

Hi,

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...

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.

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)

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.

How about AC ? - LOL

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.

ted: 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.

DVDdoug:
…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.

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.

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.

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!

ChrisTenone: 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.

ChrisTenone: 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.

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].

And, to more properly answer the actual OP question: Actual physical direction of current flow depends on the "charge carrier" involved:

  • Electrons, being negatively charged, are repelled by negative potential. Thus, they will flow from negative to positive, or from more negative to less negative. This is the most common case in electronics, as metals, which by nature, possess an ambient cloud of "free electrons", are the most prominent conductors. Even in a Semiconductor, the charge carrier is alway electronics--even in a P-type semiconductor. Holes are just a concept [conceptual charge carriers], and are actually produced by the movement of electrons.
  • Protons, being positively charged, are repelled by a positive potential, and thus move in the exact opposite way, electrons do. The closest case, in electronics, that I can think of, where protons serve as the charge carriers, is in a smoke detector that employs Americium--which gives off alpha particles. And, alpha particles are the nuclei of Helium [which contain protons].
  • Ions are considered charge carriers, but even their charge is the result of a summation of the charges on protons and electrons [and, in fact, my smoke detector example is really an example of ions as charge carriers]. Ions can have an overall charge that is positive or negative. Their direction of movement is determined by this aggregate charge. If positive, then they move towards a negative potential [or less positive potential]. If negative, vice versa.
  • Holes, as mentioned above, are conceptual charge carriers. They don't exist as a physical entity, but they are listed as a type of charge carrier. Holes always have a positive "charge", and thus, move like a proton.

We can blame Benjamin Franklin all day long for getting it wrong... but in the end... its just easier to use the "conventional" flow concept (Hole Flow, if you must) as it matches the direction that a DIODE in a schematic diagram will point.

Don't make me use diodes backward... ;-P

Ions [/i]are considered charge carriers, but even their charge is the result of a summation of the charges on protons and electrons [and, in fact, my smoke detector example is really an example of ions as charge carriers].

Another example of ions as charge carriers is in electrolyses, and in general the conductance of water.

pwillard:
Don’t make me use diodes backward… :stuck_out_tongue_winking_eye:

Not just diodes… transistors as well.

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