How does current flow in a circuit?

[mivey]

You can't say "into" a node because that implies only currents entering and not any that are leaving. Conversely, you can't say "from" a node, because that implies only those currents leaving. This is why I opted for the word "at".

Of course you can, and it implies no such thing.

 

[mivey]

I suppose it would be best to say the sum of all currents entering and leaving a node must be zero.

 

[rattus]

Who sez?

Who sez?

You can't say "into" a node because that implies only currents entering and not any that are leaving. Conversely, you can't say "from" a node, because that implies only those currents leaving. This is why I opted for the word "at".

No so Smart. One can define currents anyway one wishes. For example, it is convenient to define the currents in a wye as leaving the neutral node. If the loads are balanced, In is zero. However you define the currents though, In + Ia + Ib +Ic = 0.

It is simply a matter of phase angles and trigonometry.

 

[Mayimbe]

??? What are you getting at? Please tell me what "AC" stands for.

Alternating Current.

OK, I won't.

In the positive semi-cycle, current flows from the load to the source ...then there's what you said, too

How does the current flows from the load to the source???

The point here is there is no need to state whether the current is entering or leaving the node. In [static-] phasor/vector analysis, the phase angle takes care of that (while all magnitudes are positive).

Thats another thing. Dont know how to translate it but its call in spanish "Desacople Principle". The phase angle take care of the direction of real power, and the voltage magnitude take care of the direction of the Reactive Power (Q). Either way the current is assumed to be flowing from the source to the load, in all considerations that I have been envolved. So, it would be nice from you, to give me one example where the current is flowing from the load to the source in normal conditions.

You can if you want, but symmetrical components analysis is not required.

OK. So what is required then? And even more, who said that it was required?

Completely out of context. what I said was in response of how to deal with non linear loads, and last time I checked it was with fouriers series, and a way to do that was to take superposition (dont know if it means the same in english) by analyzing balanced systems separetly and sum all the responses in every system at the end. It has nothing to do with symmetrical components. So why did you bring that up?

Of course you can, and it implies no such thing.

Agree.

 

[Mr. Bill]

Wow, over 60 responses for a first time poster, not bad. These mathematical posts seem to cause all sorts of debate. I just wanted to answer his first question which seems to have been ignored by everyone.

How does current flow in a circuit?

Linearly. All the rest of his post seems to have been gone over enough.

 

[mivey]

Wow, over 60 responses for a first time poster, not bad. These mathematical posts seem to cause all sorts of debate. I just wanted to answer his first question which seems to have been ignored by everyone.

Linearly. All the rest of his post seems to have been gone over enough.

Factual but probably not useful to the poster. His questions were really answered within the first few posts. The rest has been more or less what the rest of us wanted to talk about.

add: mostly factual anyway.

 

[iwire]

How does the current flows from the load to the source???

Isn't the current in a circuit the same at any moment in any part of the circuit?

If we were talking DC would there only be current in one of the two conductors running to the load?

 

[Mayimbe]

Isn't the current in a circuit the same at any moment in any part of the circuit?

It depends on the nature of the circuit.

If we were talking DC would there only be current in one of the two conductors running to the load?

No. In the two of them. I see your point. The current does flows from the load to the source by the neutral.

 

[mivey]

It depends on the nature of the circuit.



No. In the two of them. I see your point. The current does flows from the load to the source by the neutral.

Not just the neutral. What about a two-wire 240 volt circuit? What do you think happens on the negative cycle? When current is flowing, pick either of the two wires and say current flows from the source to the load and I will pick the other wire and tell you it flows from the load to the source. If asked 1/120th of a second later, we would reverse our positions.

 

[LarryFine]

If asked 1/120th of a second later, we would reverse our positions.

That seems to happen a lot around here.

 

[iwire]

That seems to happen a lot around here.

:grin:

And yet other times peoples minds are locked in one postion only.


You think Mike W's ears are ringing? :grin:

 

[mivey]

You think Mike W's ears are ringing? :grin:

Nah. He can only hear the sound of his own voice. :grin:

 

[Mayimbe]

Not just the neutral. What about a two-wire 240 volt circuit? What do you think happens on the negative cycle? When current is flowing, pick either of the two wires and say current flows from the source to the load and I will pick the other wire and tell you it flows from the load to the source. If asked 1/120th of a second later, we would reverse our positions.

What cycle is the negative cycle?

I was talking about RMS currents. I said to Smart $ the same thing you are telling me now. That dont go to that aproach, the time aproach.

In fact, I will stand my view that the current does not flow from the load to the source never. Since the current has to flow on a closed circuit, the dc view that iwire proposed, still says that the current flows from the source to the load. If you are standing on the neutral perspective, you will see that the current is flowing from the load to the source. But its subjective to how you view the issue. You can stand on the loads perspective and see that the current is flowing from you to the source.

Say you draw a simple DC circuit. A source and a Resistance in serie. How does the current flows in the circuit??? From the load to the source??? Really?? so the resistance have more voltage than the source?? from where the resistance is getting that energy?? out of nowhere?? Or is it a super resistance??

 

[mivey]

What cycle is the negative cycle?

I was talking about RMS currents. I said to Smart $ the same thing you are telling me now. That dont go to that aproach, the time aproach.

In fact, I will stand my view that the current does not flow from the load to the source never. Since the current has to flow on a closed circuit, the dc view that iwire proposed, still says that the current flows from the source to the load. If you are standing on the neutral perspective, you will see that the current is flowing from the load to the source. But its subjective to how you view the issue. You can stand on the loads perspective and see that the current is flowing from you to the source.

Say you draw a simple DC circuit. A source and a Resistance in serie. How does the current flows in the circuit??? From the load to the source??? Really?? so the resistance have more voltage than the source?? from where the resistance is getting that energy?? out of nowhere?? Or is it a super resistance??

The negative cycle is when the waveform is negative relative to the reference point (on the opposite side of the zero axis from the positive side). You should know this.

Maybe it is a translation thing. Are you blending current/energy/power?

In a pure reactive load, power is flowing in for 1/2 cycle, then flowing out the other 1/2 cycle. In a pure resistive load, power is absorbed in both cycles. If the voltage and current have the same sign, then the load is absorbing energy, if the signs are different, then the load is delivering energy.

If you think current never changes direction, you are thoroughly confused. I find that hard to believe, so there must be something that is getting lost in the translation.

 

[Smart $]

Of course you can, and it implies no such thing.

I suppose it would be best to say the sum of all currents entering and leaving a node must be zero.

No so Smart. One can define currents anyway one wishes. For example, it is convenient to define the currents in a wye as leaving the neutral node. If the loads are balanced, In is zero. However you define the currents though, In + Ia + Ib +Ic = 0.

It is simply a matter of phase angles and trigonometry.

I stand by my comment. "Into" implies all currents are entering the node, while "from" implies all currents are leaving (see definitions below). The only way either of you are going to convince me otherwise is if you get Webster (or equivalent ) to change the meanings of those words. I'm just matching the words to the physics. It is impossible for all branch currents to be entering or leaving simultaneously. If one branch's current enters, at least one of the other branches' current must be leaving. The node is not a capacitor and cannot store charge. If you want to manipulate the meanings and/or the math (unnecessarily), that is your prerogative... but leave me out of it.

Furthermore, I'm not saying one can't describe the parameters as currents entering and leaving. Mostly, I am trying to point out that entering and leaving descriptions are not necessary when using static phasor analysis, The phase angle takes care of it and all magnitudes are positive, as they should be. The measurement of currents, imo, should all be "biased" the same way, i.e referenced to the node itself and using one branch current's phase angle as the 0? reference... or widen parameters to permit an outside 0? reference.

I've never said you guys can't do it however you prefer.

Merriam-Webster Collegiate? Dictionary Browse

in?to
Pronunciation: 'in-(ˌ)t?, -tə
Function: preposition
Etymology: Middle English, from Old English intō, from 2in + tō to
Date: before 12th century

1 ― used as a function word to indicate entry, introduction, insertion, superposition, or inclusion <came into the house> <enter into an alliance>
2 a : to the state, condition, or form of <got into trouble> b : to the occupation, action, or possession of <go into farming> c : involved with or interested in <into hard drugs> <into Latin epigrammatists>
3 ― used as a function word to indicate a period of time or an extent of space part of which is passed or occupied <far into the night>
4 : in the direction of <looking into the sun>
5 : to a position of contact with : AGAINST <ran into a wall>
6 ― used as a function word to indicate the dividend in division <dividing 3 into 6 gives 2>



? 2005 Merriam-Webster, Incorporated

Merriam-Webster Collegiate? Dictionary Browse

from
Pronunciation: 'frəm, 'fr?m also fəm
Function: preposition
Etymology: Middle English, from Old English from, fram; akin to Old High German fram, adverb, forth, away, Old English faran to go ― more at FARE
Date: before 12th century

1 a ― used as a function word to indicate a starting point of a physical movement or a starting point in measuring or reckoning or in a statement of limits <came here from the city> <a week from today> <cost from $5 to $10> b ― used as a function word to indicate the starting or focal point of an activity <called me from a pay phone> <ran a business from her home>
2 ― used as a function word to indicate physical separation or an act or condition of removal, abstention, exclusion, release, subtraction, or differentiation <protection from the sun> <relief from anxiety>
3 ― used as a function word to indicate the source, cause, agent, or basis <we conclude from this> <a call from my lawyer> <inherited a love of music from his father> <worked hard from necessity>

 

[iwire]

I stand by my comment. "Into" implies all currents are entering the node, while "from" implies all currents are leaving (see definitions below).

So if I say 'The women stepped into the bus' you would say that implies no one is getting out of the bus?

 

[Smart $]

So if I say 'The women stepped into the bus' you would say that implies no one is getting out of the bus?

No... but I would say that implies, of the women stepping into the bus, none are stepping out of, off, or from the bus.

 

[iwire]

No... but I would say that implies, of the women stepping into the bus, none are stepping out of, off, or from the bus.

It's killing me but I think you have me convinced.

 

[Smart $]

What cycle is the negative cycle?

I was talking about RMS currents. I said to Smart $ the same thing you are telling me now. That dont go to that aproach, the time aproach.

In fact, I will stand my view that the current does not flow from the load to the source never. Since the current has to flow on a closed circuit, the dc view that iwire proposed, still says that the current flows from the source to the load. If you are standing on the neutral perspective, you will see that the current is flowing from the load to the source. But its subjective to how you view the issue. You can stand on the loads perspective and see that the current is flowing from you to the source.

Say you draw a simple DC circuit. A source and a Resistance in serie. How does the current flows in the circuit??? From the load to the source??? Really?? so the resistance have more voltage than the source?? from where the resistance is getting that energy?? out of nowhere?? Or is it a super resistance??

This discussion is getting way beyond what I believe to be the intended scope. First, we are examining currents at a node (or junction, if you prefer). It does not matter whether the branch conductors are connected to the load or the source, or whether the currents are going source to load or load to source. All that matters is the currents going through the node under examination and their measures.

 

[mivey]

If you want to manipulate the meanings and/or the math (unnecessarily), that is your prerogative... but leave me out of it....I've never said you guys can't do it however you prefer.

If it makes it easier for you to understand, by all means stick to what you know. I prefer to define my currents in whatever manner is prudent for me at the time (and thanks for your permission to do so ).

Kirchhoff's current law can be stated both ways (actually 3 ways) and to say otherwise is just nonsense. We could site sources all day that show you are wrong to imply those that do not formulate KCL the way you do are making a mistake, but here are a few:

Slone's Standard Electrical Dictionary (1892):
When a steady current branches, the quantity of electricity arriving by the single wire is equal to the quantity leaving the junction by the branches. The algebraical sum of the intensities of the currents passing towards (or passing from) the junction is equal to zero; Summation(C) = 0 (Daniell.) In the last sentence currents flowing towards the point are considered of one sign and those flowing away from it of the other.

James Clerk Maxwell
An Elementary Treatise On Electricity (1881):
(re-stating Kirchhoff's Condition of 'continuity') At any point of the system the sum of all the currents which flow towards that point is zero.

Kendall L. Su - Georgia Tech
Fundamentals of Circuits, Electronics, and Signal Analysis-1978
Kirchhoff's current law (KCL): The sum of all currents entering any ambit at any instant must be zero.

Carter/Richardson - Univ. of Leeds
Techniques of Circuit Analysis - 1972
Kirchhoff's current law or Kirchhoff's node law, states that the algebraic sum of all the currents entering a junction point (i.e. a node) in a circuit is equal to zero

Handbook for Electricity Metering - EEI
Kirchhoff?s Current Law (KCL) can be stated in three ways:
1. The sum of the currents leaving a junction of conductors is zero at all times.
2. The sum of the currents entering a junction of conductors is zero at all times.
3. The sum of the currents entering a junction of conductors is equal to the sum of the currents leaving the junction of conductors.