Conventional vs Electron flow

Thread Starter

electricalengineer3

Joined Feb 6, 2020
60
Can someone post a simple example of solving a problem using the both of these? I get the difference between the two but I don't get how its the same if you solve either way. If someone could do some problems both ways I would much appreciate it.
 

dl324

Joined Mar 30, 2015
10,072
Welcome to AAC!

It doesn't matter which convention you use as long as you use it consistently. If you're using KCL and get a negative current, you just guessed wrong on the direction.
 

Thread Starter

electricalengineer3

Joined Feb 6, 2020
60
Welcome to AAC!

It doesn't matter which convention you use as long as you use it consistently. If you're using KCL and get a negative current, you just guessed wrong on the direction.
Yes I understand that. I am hoping to see an example of how it doesn’t matter and the technique for both ways. I can’t just say oh it doesn’t matter and understand it that way, I am hoping to see a 1to 1 comparison using both conventions.
 

BobTPH

Joined Jun 5, 2013
2,266
I don’t understand your problem. You can assign the the direction of the currents any way you want. You can have two batteries in your circuit and have one of them with the current coming out of the +terminal and the other with the current coming out of the - terminal and the solution will be the same except for the signs of the currents.

If you are getting different numbers, then you set up the equations wrong somewhere.

Bob
 

Thread Starter

electricalengineer3

Joined Feb 6, 2020
60
I don’t understand your problem. You can assign the the direction of the currents any way you want. You can have two batteries in your circuit and have one of them with the current coming out of the +terminal and the other with the current coming out of the - terminal and the solution will be the same except for the signs of the currents.

If you are getting different numbers, then you set up the equations wrong somewhere.

Bob
So lets say you set up a KVL with the current coming out of the positive of a battery and entering two resistors. -Vs +IR1+IR2=0.
Current coming out of the bottom of the battery +Vs+IR1+IR2=0, unless that is the electron current entering the resistor would still be entering the plus side of the resistor, is this not the case?
 

crutschow

Joined Mar 14, 2008
24,405
The current through a resistor is V/R where V is the voltage across the resistor and R is its resistance.

If you assume current flow, its direction is from the positive end to the negative end.

If you assume electron flow, it's direction is from the negative end to the positive end.

In either case the value is the same.

Only the assumed direction of the charge carrier flow changes.
 

Thread Starter

electricalengineer3

Joined Feb 6, 2020
60
The current through a resistor is V/R where V is the voltage across the resistor and R is its resistance.

If you assume current flow, its direction is from the positive end to the negative end.

If you assume electron flow, it's direction is from the negative end to the positive end.

In either case the value is the same.

Only the assumed direction of the charge carrier flow changes.
So the polarity of voltages and resistances doesn't change? How about with things like transistors and diodes? Is the diode connected in such a way that if it's forward biased respective to conventional current, that it is actually letting electrons flow from the - side?
 

nsaspook

Joined Aug 27, 2009
6,960
So why would the electron current be entering the minus side of the resistor. Also, would the current be coming out of the minus side still be listed as 2A and not -2A?
Forget about electrons, really, they don't matter in basic circuit theory (learned conventional flow in school and electron flow in the military). Conventional current is compatible with Passive sign convention. This is what you will learn and use even when the physical movement of charges is important to understand the internal operation of devices.
To comply with the convention, the direction of the voltage and current variables used to calculate power and resistance in the component must have a certain relationship: the current variable must be defined so positive current enters the positive voltage terminal of the device.[3] These directions may be different from the directions of the actual current flow and voltage.
https://web.archive.org/web/20120916231820/http://web.cecs.pdx.edu/~prasads/BasicConcepts.pdf
 
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crutschow

Joined Mar 14, 2008
24,405
How about with things like transistors and diodes? Is the diode connected in such a way that if it's forward biased respective to conventional current, that it is actually letting electrons flow from the - side?
Yes.
Conventional current flow is in the direction of the diode arrow.
Electron flow is opposite the arrow direction.

It's similar for bipolar transistors.
Conventional flow is in the direction of the base-emitter arrow.
Electron flow is opposite the base-emitter arrow direction.

That's the reason I like conventional current for my circuit analysis.
The currents in solid-state devices all go in the direction of the arrows, and in schematics the flow is typically from top (the power plus side) to bottom (ground or the power minus side).

One device type that really needs electron flow for understanding of their operation are vacuum (electron) tubes, since the electrons are emitted by the hot cathode and flow to the anode.
 
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Thread Starter

electricalengineer3

Joined Feb 6, 2020
60
Of course not. Choosing electron current does not make your battery’s positive terminal negative. The voltages and polarities are not affected.

Bob
So is a voltage source labeled in such a way that the plus side (higher potential) is labeled for the effect on positive charge carriers. Therefore, a positive charge at the top of a battery feels high potential and flows to the negative. Wouldn't it make more sense for electrons to be positive charge and be at the plus side of the battery and flow to low potential since they are actually what is carrying the charge in a wire?
 

Thread Starter

electricalengineer3

Joined Feb 6, 2020
60
Forget about electrons, really, they don't matter in basic circuit theory (learned conventional flow in school and electron flow in the military). Conventional current is compatible with Passive sign convention. This is what you will learn and use even when the physical movement of charges is important to understand the internal operation of devices.


https://web.archive.org/web/20120916231820/http://web.cecs.pdx.edu/~prasads/BasicConcepts.pdf
So passive sign convention is based on the fact that current leaves the positive terminal of a source? With things like Ohm's law and such why do people say there would just be more negatives if we used electron flow? Wouldn't these equations still be the same just with a different sign convention?
 

Thread Starter

electricalengineer3

Joined Feb 6, 2020
60
Forget about electrons, really, they don't matter in basic circuit theory (learned conventional flow in school and electron flow in the military). Conventional current is compatible with Passive sign convention. This is what you will learn and use even when the physical movement of charges is important to understand the internal operation of devices.


https://web.archive.org/web/20120916231820/http://web.cecs.pdx.edu/~prasads/BasicConcepts.pdf
Also, since you mentioned you were in the military, could you show me a few problems and how you would solve them using electron vs. conventional flow? And is the polarity of voltage also a convention as the + side is the side with higher potential that would push conventional flow out?
 
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