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I have always stumbled when remembering which current flow notation to use. In my mind, it's by default conventional current flow.

Conventional flow notation

But, I also have in mind electron flow notation.

Electron flow notation

Do you know of a mnemonic (i.e. a quick memory trick) to remember the direction of current flow?

According to the Wikipedia Anode article, "A common mnemonic is ACID, for "anode current into device", but I feel like there might be a better one for beginners.

Nick Bolton
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    Apparently when they made the first battery, they labelled the terminals + & -... Just chance they got them the "wrong" way round. – Solar Mike Jul 06 '21 at 13:16
  • I like Mat’s answer. I don’t know what tricks your mind . How about plus= extrovert , minus = introvert, if they collide = hadron – Tony Stewart EE75 Jul 06 '21 at 13:17
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    The only time you'd need to worry about electron flow is if you're designing a vacuum tube--just don't bother with it. – Hearth Jul 06 '21 at 13:36
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    I remember that electrons repel each other, next thought is that minus terminal has "excess" electrons, so that is where they move out of. – Wesley Lee Jul 06 '21 at 14:01
  • I have this mnemonic: "From plus to minus". Works great :) Also you can remember the picture you have posted visually. Battery is usually oriented like this, so you probably won't forget it. Then the current goes up and returns from the ground that is usually on the bottom. Electrons flow is just the opposite (so the "opposite" mnemonic works well too). – Eugene Sh. Jul 06 '21 at 14:04
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    You can't assume that current (conventional or electron) always flows the same way through a battery, much less through an ideal voltage source. Conventional current can flow either way through a battery or an ideal voltage source. If you make these assumptions now you will be very confused later. – Elliot Alderson Jul 06 '21 at 16:54
  • If you connect another cell with higher voltage in series opposition with the cell in the circuit, your 'tricks' may lead you wrong. So no point in remembering such 'tricks'. – Mitu Raj Jul 06 '21 at 19:01
  • Just remember that electron holes flow from positive to negative. – Glen Yates Jul 06 '21 at 21:58
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    @Hearth electrons diffuse faster than holes, so being aware of electron flow is useful in high-speed semiconductor design. I wouldn’t be so quick to dismiss it. – Frog Jul 07 '21 at 07:20
  • For "ACID" you have to remember what the anode is, which I find much harder. For me it's easier to remember that conventional current is the wrong way around. (Actually I refuse to say anything flows from plus to minus. In my head the sign of I is just conventionally as if the current was flowing from plus to minus ;-) ) – jdm Jul 07 '21 at 10:32
  • Plus means there's a surplus. It flows to minus where there is a deficiency. Simple economics. – Spehro Pefhany Jul 07 '21 at 18:30

8 Answers8

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Your default is correct. Conventional current flows from positive to negative. We draw our schematics as you have with positive rail at the top. Current then flows from top to bottom. You seldom need electron flow to analyse practical circuits.

If you like, positive charges flow out of the top and negative (electrons) flow out of the bottom.

COUP: Current Out Of Positive

DWEF: Don't Worry About Electron Flow

Transistor
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Why do you need to know the flow direction of electrons?

If you're dong electrochemistry, then the charge of the ions involved is explicit, and they flow both ways anyway.

It is necessary if you're doing a Hall experiment to know what charge the mobile carriers in the material are carrying, and then choose the right direction for the relevant charge.

However, 99.9% (estimated) of electrical engineering can be done with conventional charge.

FWIW, ACID doesn't really help me when connecting diodes, TL431s, LEDs etc. I've got to look up a diagram to identify the pins. I might as well check what current flow direction is required while I'm there.

Can you remember that electrons have a negative charge? If so, then they flow opposite to the direction of conventional current.

Neil_UK
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  • What about vacuum tubes? – Hot Licks Jul 06 '21 at 21:55
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    @HotLicks What about vacuum tubes? Electrons are negative so they flow opposite to the direction of conventional current. – Neil_UK Jul 07 '21 at 04:41
  • Vacuum tubes are what showed that Benjamin Franklin got it backwards. – Hot Licks Jul 07 '21 at 12:07
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    @HotLicks Franklin didn't have vacuum tubes. Vacuum tubes happen to work on electrons, but current flow can be ions, holes or positrons, too. Franklin didn't get it backwards: he defined a convention. The physics doesn't give you a forward or backward. – John Doty Jul 07 '21 at 14:21
  • Franklin got it backwards because he didn't have vacuum tubes. – Hot Licks Jul 07 '21 at 16:55
  • @HotLicks https://physics.stackexchange.com/questions/17109/why-is-the-charge-naming-convention-wrong – Bergi Jul 07 '21 at 23:54
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    @HotLicks The real error made by most beginners is thinking that "an electric current means electrons are moving," and also they often have the wrong idea that the electrons move at the speed of light, (e.g. when you switch on a light, electrons magically rush down the wires all the way from the power station 100 miles away to make it light up) when in reality they are only drifting fractions of an inch per second. – alephzero Jul 08 '21 at 03:00
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Just remembering that current goes from positive to negative is easier than trying to work out some mnemonic for it.

Forget what the electrons are doing, unless you are actually designing semiconductors.

Simon B
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On LED's the Cathode is flat (there's often a flat spot on the physical device and on the symbol, the arrow goes into a flat line), and ground is flat -- so the cathode is the low side of the device!

Scott Seidman
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Frankly, I've always found it easier to remember a simple fact: "Current flows downhill."

JBH
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For conventional current, think of a battery as a waterfall where gravity pulls the water to ground.

For electron flow, think of a battery as a vacuum cleaner where electrons are sucked in at the top and blown out at the bottom.

tim
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  • Except that a battery can be charged as well as discharged, so current and electrons can flow either direction. It's best not to make these kinds of assumptions based solely on the type of circuit element. – Elliot Alderson Jul 06 '21 at 16:52
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As others have said forget electron flow and just use conventional current. For a quick memory trick if your circuit has BJTs, diodes, LEDs, SCRs... the arrow in their symbols indicates the direction of current flow. As it happens this corresponds to P-type to N-type, similar to the current flowing positive to negative.

There are exceptions to the "arrow" trick, for example the current generated in a photo diode is against the arrow, but as a general rule it works well.

Ken Mercer
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Current doens't flow, it's a phenomenon that occurs in a resistive material. A physical quantity pointing the relationship of V/R
That is current, the phenomenon of excited electrons in a resistor producing electron flows in both directions.
The case for PN junctions is quite different since PN junctions are not resistive but possess a dielectric which finally flow to the lowest potential point of the PN connection.

nick
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    Hi, Nick. This doesn't really answer the question at the top of the page and seems to be more of a ramble. "Current doesn't flow ..." Yes it does. It's measurable and observable in all sorts of ways including electron beams and electro-chemical reactions. You have many spelling mistakes. If English is not your first language then please mention this in your user profile. – Transistor Jul 07 '21 at 18:51
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    Regarding your edit, "... excited electrons in a resistor producing electron flows in both directions." This is not correct. In metallic conductors the mobile charge carriers are electrons. When a current is flowing the general electron drift is from negative to positive. The electrons will drift at a speed in the order of mm/s. Current can't flow in both directions simultaneously. – Transistor Jul 07 '21 at 19:03
  • it's a fact. current is a bounce-back phenomenon in a electron-flow permissive material. – nick Jul 07 '21 at 19:05
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    Can you reference an article where we can read up on the bounce-back phenomenon? – Transistor Jul 07 '21 at 19:12
  • Check out for Faraday studies on dielectrics. i'm sure there is at least one or two reading materials on how electrons behave (in metals basically). Copper was popular at the time and is one of the metals which also has high electron bounces, since a potential electron jump generates a hole and a moving electron but also has a probability of not jumping and accumulating extra electrons in a same orbits which flow practically in any directions; That studies are posterior to Faraday but are product of Faraday's and Maxwell work, thus it can be read in Faraday papers. – nick Jul 07 '21 at 19:20
  • Electrical conductors such as metals are not dielectrics. I think it's up to you to support your claim, not for us to research it. Copper is still popular. – Transistor Jul 07 '21 at 19:23
  • Here you go: https://www.quora.com/What-is-the-dielectric-constant-of-copper https://en.wikipedia.org/wiki/Relative_permittivity – nick Jul 07 '21 at 19:24
  • Thanks for the link. I read there, "*Dielectric constant, as the name suggests, is a property of dielectrics, which are non-conducting materials. In simple terms Dielectric constant ( ϵr ) is a measure of the energy storing capability of the material in the form of electric field, or in other words, the ability of the material to get polarized by the electric field (separation of oppositely charged species). Neither of these is applicable for a metal which conducts electricity freely (no charge separation possible).*" – Transistor Jul 07 '21 at 19:30
  • The property from which electricity flows is called Coulomb force, conductivity don't exist in vacuum. All materials are equally permissive and/or resistive in vacuum and how their electrostatic charges (atomic potential diferential) behave defines their dielectric constant (charge potential interaction) which is a physical measure, unlike conductivity which is a electrical engineering terminology. – nick Jul 07 '21 at 19:36