0
\$\begingroup\$

If Conventional Current is backwards, how do I look at something like this schematic and trace the flow of current? I'd like to follow the design linearly from positive to negative.

enter image description here

When the battery is on, does current go to 8, then 4, then through R1 and so on?

Does the current get "back around" to the side of the capacitor, 1, and the speaker eventually (though fast)?

How can this be so if in reality electrons flow from negative to positive?

Edit: If the current were water here, how would I see that physically on the wiring, as if they were pipes?

\$\endgroup\$
14
  • 12
    \$\begingroup\$ Conventional current is not wrong. It is just conventional. So use it for the conventional analysis. Just forget about the "wrong" thing, it will only confuse you. \$\endgroup\$
    – Eugene Sh.
    Jul 18, 2017 at 17:15
  • 1
    \$\begingroup\$ @GregoryKornblum I highly doubt anyone is using a different convention... That would produce too much mess when interfacing with other engineers and literature.. \$\endgroup\$
    – Eugene Sh.
    Jul 18, 2017 at 17:23
  • 1
    \$\begingroup\$ By the way, from when i was eight i wondered how the heck the switch on the wall knows how many electrona to give to the lamp a moment after it is switched, when the lamp is still off. Took me 15 years to understand :) \$\endgroup\$
    – user76844
    Jul 18, 2017 at 17:26
  • 6
    \$\begingroup\$ Reminds me of when I was insisting on electron-flow. Eventually, I just "broke" and went with the lemmings, instead. ;) To the OP, you just need to give it up and go with the flow, so to speak. As far as understanding things, tracing currents alone in most useful cases won't give you "understanding." Instead, it's how those currents behave, moment to moment, that often counts the most. And that just takes time to develop -- a never-ending process of learning that will hopefully continue to improve until you die. \$\endgroup\$
    – jonk
    Jul 18, 2017 at 17:37
  • 1
    \$\begingroup\$ @johnny if you're trying to trace the flow of signal on very short timescales, then it propagates from both the negative and positive at the same time - and it's made of electromagnetic fields. The fields eventually bring electrons along with them, but it's the field that matters. Becomes clearer if you think of a very long Ethernet cable: when you send a pulse, it goes on both parts of a pair, not all the way out on one and back on the other. \$\endgroup\$
    – pjc50
    Jul 19, 2017 at 8:26

4 Answers 4

7
\$\begingroup\$

Conventional current being backwards from electron flow has no effect whatsoever on circuit analysis. If you really wanted, you could swap the signs on all your currents and voltages and the math would work out the same, but people would be confused.

If you're doing an ad-hoc intuitive analysis without any math, well, it still doesn't matter whether you start at the positive end or the negative end of things, or neither.


The behavior of currents flowing in wires and through components can and should be be understood symmetrically — positive and negative voltages/currents, or electrons and “holes”, being equal and opposite to each other.

The causality, the ways changes propagate around a circuit, is also symmetric. If you close a switch or make some other such change, the changes in voltage and current propagate away from the switch along both connected wires — with opposite signs, but otherwise completely identical, at the same speed.


Specific components (diodes, ICs, capacitors, tubes…) may have polarity, so they require or only allow a flow with a specific direction/sign, but it does not actually matter at all for understanding the behavior of the circuit which one matches the actual flow of electrons — only if you want to understand why the components do what they do does that begin to matter.

\$\endgroup\$
2
  • \$\begingroup\$ Kevin, I've been thinking about this answer. It appears to me that slow people (that's me) take for granted they are dealing with a circuit. KCL,etc.are principles of a circuit starting and ending with "charge." So what I started thinking was, no matter what, the circuit is, well, a circuit, a closed loop that is, well, closed and charge is "flowing." The whole thing is conducting. Somehow, somewhere, whatever, charge will end up at the end of the circuit. When I start to control the electrons, deciding which pieces goes where to bring an idea to reality, then I use loop analysis, etc. \$\endgroup\$
    – johnny
    Jul 20, 2017 at 14:00
  • \$\begingroup\$ @johnny The electrons can only move if there's a place for them to go, which means you also have to control the places for them to go. \$\endgroup\$
    – user253751
    Mar 29, 2018 at 4:26
10
\$\begingroup\$

if Conventional current is wrong

Conventional current: used by engineers and physicists everywhere. It's what's measured by ammeters! It applies to all circuits, including the non-electron flows in dirt, nerves, acids, plasmas, etc.

"Electron current:" used by technicians during WWII ...and by several generations of students taught by them. Applies to solid metals, and especially to vacuum tubes. It cannot explain nerves and batteries, semiconductors and plasmas, or any situation where proton-flows or mobile ions are paramount.

In other words, electron current is wrong. Don't use it. If you have a textbook which employs backwards current (electron current,) just throw it away. Heh, or perhaps chop it up, so it cannot harm anyone.

how can I trace the flow of current in a schematic?

To understand circuits, we don't trace the flow. (After all, batteries don't spit out constant current.) Instead, we study the schematic as a whole, and determine the pattern of voltages across the various circuit points. Then, knowing the voltages, we can figure out the current in any component.

"Tracing the flow" doesn't work, since it isn't based on Ohm's Law, and it leads to mistaken thinking. For example, at any "Y" junction, how do the charges know to split up? How do they know which path to take? They don't. Instead, the voltages far downstream are determining the current in the entire circuit.

Also, to visualize the flow, we DON'T start at the power supply. After all, the wires are already filled with electrons. Current is like a flywheel or drive-belt, so we can start at any point on the circle. That's why the currents aren't simple and obvious: a schematic is like a bunch of flywheels, all loosely coupled together and spinning at different rates. (A battery isn't a source of electricity; a battery is actually an "electricity pump.")

If tracing the flow doesn't lead to understanding, then what does? Ah, that would be voltage, as well as the voltage-dividers scattered throughout the circuitry. The goal of electronics students is to learn to "see the voltages" all throughout a schematic.

One education site which goes into the voltage-divider viewpoint is NCSU/Williamson:

http://web.archive.org/web/20151113155539/williamson-labs.com/transistors/transistors-main.htm#animations

Also check out Falstad's java circuit simulator, where voltages are shown as colors. Here's the animated guts of a 555:

http://www.falstad.com/circuit/e-555int.html

ALso see his entire circuit-animations index.

\$\endgroup\$
6
  • \$\begingroup\$ Vacuum tubes, right! \$\endgroup\$
    – user76844
    Jul 18, 2017 at 18:13
  • \$\begingroup\$ "electron current is wrong" Heh, in my Navy Electronic Schools (ET "A" and ET "B" in the late 70s) we were taught just the opposite, and laughed at the poor electrical engineers who had to still pretend a known falsehood based on old tradition. I just assumed ya'll thought it would be too expensive to update all the old books and papers. Either that, or it was like a religious belief or something. ;) \$\endgroup\$
    – RichF
    Nov 3, 2018 at 22:01
  • \$\begingroup\$ @RichF Yep, definitely religious. Only, it's about TWO DIFFERENT beliefs: electron-believers versus the engineers. Physics says that protons flow just fine (but only in acids, and in salt water, nerves/brains etc.) The Electron Religion insists that all currents are electron-flows, and that protons never flow. They're right, but only when looking at metal wires and spark discharges. For non-metals, the vast majority have no free electrons, and exactly zero electron-currents. Electrons never flow through human bodies, through battery electrolyte, or through the ground (damp dirt.) \$\endgroup\$
    – wbeaty
    Mar 12, 2021 at 23:54
  • \$\begingroup\$ @wbeaty I'm pretty sure there's ion flow in sparks. \$\endgroup\$
    – Hearth
    Mar 13, 2021 at 0:26
  • 1
    \$\begingroup\$ Here's the rub (and the reason for the DV): you need to consider both holes and electrons when digging into semiconductor physics, otherwise you'll have a horrible time as soon as you start dealing with BJTs due to the fact they rely on minority carriers as part of their operation \$\endgroup\$ Mar 13, 2021 at 0:58
2
\$\begingroup\$

If Conventional Current is backwards, how do I look at something like this schematic and trace the flow of current?

The convention that current flows from + to - was agreed on long before the discovery of the electron by J J Thompson in 1898. It worked in all their calculations then and still works now.

In your schematic you have correctly drawn the positive rail at the top and the negative at the bottom as is favoured by most electronics designers. Current then (generally) flows from top to bottom.

enter image description here

Figure 1. Conventional current vs electron flow. Both move simultaneously with equal effect - just in opposite directions. Source: Electrical Market Plus.

To analyse your circuit you would need a diagram of the internals of the 555 to understand how it switches when voltages change at its terminals.

Start with basic circuits and build up. It's a fascinating subject that you can spend a lifetime studying and continue to learn new things every day.

\$\endgroup\$
0
\$\begingroup\$

In your schematic, conventional current flows from the battery + terminal to the 555 pin 4 AND 555 pin 8 AND R1 simultaneously.

Any further analysis of current flow in that circuit requires a study of the internal workings of the 555 IC.

Forget the "water analogy" (and any other analogy you find), as it is only useful in very limited situations, and can be confusing or misleading otherwise.

\$\endgroup\$
1
  • \$\begingroup\$ The water analogy is great for understanding circuits intuitively and correctly. I don't understand why people say otherwise. \$\endgroup\$
    – endolith
    Jan 9, 2018 at 20:54

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.