Nope. You can flip a coin.

Consider the following assignments for the voltages and currents in each component in the circuit:

View attachment 198911

Note that I avoided using V1 and V2 since these are the symbolic voltages of the two given supplies.

These were literally made by flipping a coin for each current and each voltage polarity. Absolutely no attempt was made to pick the "right" directions. We therefore have ten unknowns (two for each component -- a voltage and a current) that we have to solve for. So we need ten linearly independent equations.

In terms of these symbolic voltages, we can apply KVL around any closed loop in the circuit. For each loop we sum the voltage gains (or drops) going around the loop. We can flip a coin to determine if we sum the gains or the drops and we can flip a coin to determine if we go clockwise or counterclockwise around the loop.

Left loop: (+V6) + (+V7) + (-V3) = 0 [Sum of voltage gains going clockwise starting at A]
Right loop: (-V3) + (-V4) + (-V5) = 0 [Sum of voltage drops going clockwise starting at B]
Perimeter: (-V6) + (-V5) + (-V4) + (-V7) = 0 [Sum of voltage gains going counterclockwise starting at A]

We can use any two of these, since the third is a linear combination of the other two. For instance, if you add the equations for the Left and Perimeter loops, you get the equation for the Right loop.

In terms of these symbolic currents, we can apply KCL at every node in the circuit. For each node we sum the currents into (or out of) the node and set it equal to zero. We can flip a coin to determine if we sum the currents into or out of the node.

Node A: (+I5) + (-I1) = 0 [Sum of currents into the node]
Node B: (+I1) + (+I2) + (+I4) = 0 [Sum of currents into the node]
Node C: (-I2) + (-I3) = 0 [Sum of currents into the node]
Node D: (+I5) + (+I4) + (-I3) = 0 [Sum of currents out of the node]

We can use any three of these; the fourth is a linear combination of the others. For instance, if we sum the equations for Nodes A, B, and C, we get the equation for Node D.

For all of these equations, the choice of conventional current or electron current is completely immaterial (as long as we are consistent and use the same definition for all of the currents in the circuit).

So our KVL and KCL equations give us five of the ten equations we need. The other five come from the constitutive equation for each component, which relates the voltage across that component to the current through that component.

V6 = V1
V7 = (-I1)·R1
V3 = (-I4)·R3
V4 = (+I2)·R2
V5 = -V2

This is where the choice of current convention can come into play. The above equations are for conventional current and they would also apply to electron flow IF the electron-flow crowd were internally consistent. But they aren't, and so they need to apply a minus sign to the three middle equations (the Ohm's Law equations).

With these ten equations we can now solve for every voltage and current in the circuit.

Not surprisingly, if this is the way we solved circuits in practice, we would almost never get correct results because there are just too many opportunities to make silly mistakes. So we develop analysis techniques the embed most of the constraints into the technique itself. For example, Node Voltage Analysis is merely a systematic application of KCL in such a way that KVL is guaranteed to be satisfied and the constitutive equations are taken into account. Similarly, Mesh Current Analysis is merely a systematic application of KVL in such a way that KCL is guaranteed to be satisfied and, again, the constitutive equations are taken into account.

Okay, I understand everything you're saying. Let me get into your way of thinking. When you say this is where the choice of current convention can come into play, and the part about applying to electron flow. What about conventional current and electron flow makes you say that?

 

Two answers to two separate questions:

1) It does not matter if you use electron flow or conventional current, the end result is the same.

2) The example shows that the direction of the current is not dictated by the polarity of the voltage source. Current can happen to flow in either direction.

 

Two answers to two separate questions:

1) It does not matter if you use electron flow or conventional current, the end result is the same.

2) The example shows that the direction of the current is not dictated by the polarity of the voltage source. Current can happen to flow in either direction.

I’ll answer by first saying I understand your 2nd point. My final questions are what does it mean to use electron flow or conventional current? Which did I use to solve and what would change if I used the other way? What was the final answer I got in?

 

Okay, I understand everything you're saying. Let me get into your way of thinking. When you say this is where the choice of current convention can come into play, and the part about applying to electron flow. What about conventional current and electron flow makes you say that?

Using conventional current (the left diagram), if we pick the direction correctly in terms of the direction that charge flows, then the resulting current will be a positive value.

Using electron-current done properly (the middle diagram), if we pick the direction correctly in terms of the direction that the electrons flow, then the resulting current will be a negative value.

Notice that if I were to give you either of the left two diagrams with no label above it, you couldn't tell the difference between choosing conventional versus electron current or just guessing the actual direction of the current correctly versus incorrectly.

But the people that insist on using electron flow almost invariable do NOT do it properly. They would use the right diagram and insist that it is correct even though it results in them needing to use magical mystery minus signs in order to get a positive current to move a negative amount of charge.

 

View attachment 198938

Using conventional current (the left diagram), if we pick the direction correctly in terms of the direction that charge flows, then the resulting current will be a positive value.

Using electron-current done properly (the middle diagram), if we pick the direction correctly in terms of the direction that the electrons flow, then the resulting current will be a negative value.

Notice that if I were to give you either of the left two diagrams with no label above it, you couldn't tell the difference between choosing conventional versus electron current or just guessing the actual direction of the current correctly versus incorrectly.

But the people that insist on using electron flow almost invariable do NOT do it properly. They would use the right diagram and insist that it is correct even though it results in them needing to use magical mystery minus signs in order to get a positive current to move a negative amount of charge.

Well isn't that far right diagram because the charge is negative AND the direction is negative?

 

Well isn't that far right diagram because the charge is negative AND the direction is negative?

What does it mean for the direction to be negative?!!!

If the direction is negative in the right diagram, why isn't the direction negative in the middle diagram?

In the diagram I included in Post #117, which of those currents are in negative directions?

 

What does it mean for the direction to be negative?!!!

If the direction is negative in the right diagram, why isn't the direction negative in the middle diagram?

In the diagram I included in Post #117, which of those currents are in negative directions?

The direction is negative in the middle diagram, but it doesn’t account for direction and the sign on the charge. Even if you define positive direction the other way, out of the negative terminal, there would be negative charges in a positive direction or you could think of it as positive charges in the negative direction. From both terminals though the value seems to be the same including the sign

 

The direction is negative in the middle diagram, but it doesn’t account for direction and the sign on the charge. Even if you define positive direction the other way, out of the negative terminal, there would be negative charges in a positive direction or you could think of it as positive charges in the negative direction. From both terminals though the value seems to be the same including the sign

You seem to think that you have some means of determining whether the direction assigned to a current is positive or negative. Well, if that's the case, then you better be able to make that determination for any current in any diagram.

So, in the following diagrams, is the current defined in the positive or the negative direction (and why)?


If you can't unambiguously determine what direction those two currents are defined in (as far as positive or negative), then perhaps it's because the whole notion of a current definition being in the positive or negative direction is without meaning.

 

You seem to think that you have some means of determining whether the direction assigned to a current is positive or negative. Well, if that's the case, then you better be able to make that determination for any current in any diagram.

So, in the following diagrams, is the current defined in the positive or the negative direction (and why)?

View attachment 198942View attachment 198943
If you can't unambiguously determine what direction those two currents are defined in (as far as positive or negative), then perhaps it's because the whole notion of a current definition being in the positive or negative direction is without meaning.

You’re right it would always be ambiguous, this is what I thought the whole point of conventional current was. I mean if the whole direction thing is ambiguous then why did Ben Franklin even have to decide a direction in the first place?

 

You’re right it would always be ambiguous, this is what I thought the whole point of conventional current was. I mean if the whole direction thing is ambiguous then why did Ben Franklin even have to decide a direction in the first place?

Ben Franklin didn't decide a direction.

In about 1750 (long before the discovery of the electron) he undertook a number of experiments in which he rubbed various materials against each other. In addition to noting that if he rubbed A against B that A and B would be attracted to each other, he also noted that if he rubbed A against B and also C against D, that if A was attracted to C then it would be repelled by D and that B would then be repelled by C and attracted to D. From this he surmised that objects possessed some kind of "electric fluid" and that, normally, they had just the right amount of fluid to keep them from being attracted or repelled by other objects but that rubbing them together transferred some of this fluid from one object to the other. Objects with a surplus of fluid will attract objects with a deficiency of fluid, but two objects with a surplus will repel and two objects with a deficiency will repel.

When rubbing a glass rod with silk, he arbitrarily declared that the glass rod has an excess of electric fluid and was thus positively charged (while the silk, having a deficiency of fluid, would be negatively charged). Although I'm aware of no paper in which he explains his rationale for this choice (it could have be a coin toss), it makes some sense to think that whatever this fluid was that it would more easily come off of the silk cloth and go onto the glass rod than the other way around.

In the nearly half century that elapsed between Franklin's work and Thomson's discovery of the electron in 1897 the scientific community had adopted Franklin's choice since there was no reason to do otherwise and every reason to be consistent so as to all be on the same page in their writings.

In actuality, when you rub glass with silk electrons are transferred from the glass to the silk leaving a deficiency of electrons on the glass and a surplus of electrons on the silk and thus electrons are negatively charged.

 

Ben Franklin didn't decide a direction.

In about 1750 (long before the discovery of the electron) he undertook a number of experiments in which he rubbed various materials against each other. In addition to noting that if he rubbed A against B that A and B would be attracted to each other, he also noted that if he rubbed A against B and also C against D, that if A was attracted to C then it would be repelled by D and that B would then be repelled by C and attracted to D. From this he surmised that objects possessed some kind of "electric fluid" and that, normally, they had just the right amount of fluid to keep them from being attracted or repelled by other objects but that rubbing them together transferred some of this fluid from one object to the other. Objects with a surplus of fluid will attract objects with a deficiency of fluid, but two objects with a surplus will repel and two objects with a deficiency will repel.

When rubbing a glass rod with silk, he arbitrarily declared that the glass rod has an excess of electric fluid and was thus positively charged (while the silk . Although I'm aware of no paper that explains his rationale for this choice (it could have be a coin toss), it makes some sense to think that whatever this fluid was that it would more easily come off of the silk cloth and go onto the glass rod than the other way around.

In the nearly half century that elapsed between Franklin's work and Thomson's discovery of the electron in 1897 the scientific community had adopted Franklin's choice since there was no reason to do otherwise and every reason to be consistent so as to all be on the same page in their writings.

In actuality, when you rub glass with silk electrons are transferred from the glass to the silk leaving a deficiency of electrons on the glass and a surplus of electrons on the silk and thus electrons are negatively charged.

Aha so we just think of positive current as the flow of charge or more specifically the flow of positive charge? I’m still confused on the far right diagram though why that wouldn’t be the correct way of looking at electron flow?

 

Aha so we just think of positive current as the flow of charge or more specifically the flow of positive charge? I’m still confused on the far right diagram though why that wouldn’t be the correct way of looking at electron flow?

Go back to the example I used a long, long time ago in a galaxy far, far away.



If the initial current flowing into the green node is 10 A (which, by the universally-agreed-to definition of an ampere, is 10 coulombs per second) and if that current decays but is always flowing into the green, then how is it that we can end up with a charge of -10 coulombs on the green node when everything is said and done?

Answer: We need to apply a magical mystery minus sign in order to get things to work out!

 

I take it with a grain of salt and some common sense. You will continue to see it both ways depending on the document you are reading so get familiar with it. Once I became used to it, it became a non-issue.

 

The current flow is always from the + to the -, Kirhov's 2 laws just show us how the current is divided in every node. The current that comes in the node, must always equal the current that goes out.


I strongly disagree with these statements, I don't meant to insult anyone, but the western education reformation has lead american properly = real wrong.

There are several statements there. Which statement(s) do you disagree with, in what way do you disagree with it(them), what do you believe is(are) the correct statement(s) in its(their) place, and what is your argument supporting its(their) correctness?

What is wrong with the left statement? It shows current (i.e., the flow of charge) going from positive to negative. So what is it that you disagree with?

What is wrong with the middle statement? It shows current (i.e., the flow of charge) going from positive to negative. So what is it that you disagree with?

What is wrong with the right statement? It shows current (i.e., the flow of charge) going from negative to positive and it is stated that this, while typically used by the electron-flow crown, is not proper. So what is it that you disagree with?

Whatever the shortcomings of the western educational system, it would appear that your educational system also has flaws if it embodies the notion that just declaring disagreement with some unspecified statement constitutes proof that the statement is wrong.

 

Go back to the example I used a long, long time ago in a galaxy far, far away.

View attachment 198953

If the initial current flowing into the green node is 10 A (which, by the universally-agreed-to definition of an ampere, is 10 coulombs per second) and if that current decays but is always flowing into the green, then how is it that we can end up with a charge of -10 coulombs on the green node when everything is said and done?

Answer: We need to apply a magical mystery minus sign in order to get things to work out!

Well what I don't get then is how is electron flow any different then normal current? If we say that 10A (conventional) comes out of the positive and -10A(electron flow) comes out of the negative we're saying the exact same thing. No need to change signs or anything

 

I don't want to argue, I deleted my post. Please do the same and delete your quotation as well. I say you are right and move forward.

 

Well what I don't get then is how is electron flow any different then normal current? If we say that 10A (conventional) comes out of the positive and -10A(electron flow) comes out of the negative we're saying the exact same thing. No need to change signs or anything

I have said, repeatedly, that it ISN'T any different!

I have also said that people that prefer to use what they call "electron-flow" or "electron current" almost always do it wrong, thus creating the illusion that there is a difference.

 

Well what I don't get then is how is electron flow any different then normal current? If we say that 10A (conventional) comes out of the positive and -10A(electron flow) comes out of the negative we're saying the exact same thing. No need to change signs or anything

Therein lies your problem. I have yet to see anyone who uses electron flow use a negative sign when indicating the flow of negative current.

 

Therein lies your problem. I have yet to see anyone who uses electron flow use a negative sign when indicating the flow of negative current.

Which is why they have to use magical mystery minus signs in order to get things to work out.

How else can a positive amount of coulombs per second flowing onto an initially uncharged plate of a capacitor yield a negative number of coulombs on that plate?

 

I have said, repeatedly, that it ISN'T any different!

I have also said that people that prefer to use what they call "electron-flow" or "electron current" almost always do it wrong, thus creating the illusion that there is a difference.

Okay so its literally the same convention as what we already have? The thing that is weird is when some people explain electron flow or when you look at military material, they act as if the current coming from the -(electron flow) is positive since it has a negative charge and is going in the opposite direction, so two negatives making a positive