Voltage vs Current Which Occurs first?

Ya’akov

Joined Jan 27, 2019
9,079
I think there is some confusion as to what i mean when i say simultaneous.

I am not saying that current reaches it's highest point instantaneously. I am saying that current STARTS to flow as soon as voltage is applied. It is the start point, at t=0, that i am talking about, not 1ps later or 1us later although we could look at that too.
Nothing can start when no time has elapsed. Starting means something has happened, when 0 seconds have elapsed nothing has started. While "which comes first" appears fo have changed meaning, since it seems incontestable that electric potential exists without a circuit and current only exists with a circuit...

So i think we can say a voltage can exist by itself but not sure if that applies to a transistor circuit or other circuit.
WE now have a new question, and the answer probably has something to do with the Plank Length and possibly the velocity factor.

In any case, and your raising of a transistor makes me wonder what you are actually thinking about. When to apply a voltage to the transistor's base, current flows with only the "delay" that is defined by whatever threshold we arbitrarily settle on. Let's just say the deal is equal to the time it takes for the first electron to move \( ℓ_p \) (1.616255(18)×10−35 m) which would happen in very close to \( 5.39×10^{-44} \) seconds. That would be one Planck Length in one Planck Second.

That current will be flowing to the base, that current is not yet flowing between collector and emitter seems entirely unrelated to the question at hand.

I must admit it is a little bit off-putting to read you saying:

am starting to think now though that some people will never grasp this concept [...]
when I believe you haven't presented a cohesive argument for your assertions and you reject—without relevant counterarguments—cogent objections to what you appear to be saying. It comes off as arrogant and insulting to say "you just don't understand" while from this perspective, your assertions don't have logical consistency.

I wish you would reconsider that. At this point, I will retire from the conversation and ignore the thread.
 

Thread Starter

MrAl

Joined Jun 17, 2014
11,396
Nothing can start when no time has elapsed. Starting means something has happened, when 0 seconds have elapsed nothing has started. While "which comes first" appears fo have changed meaning, since it seems incontestable that electric potential exists without a circuit and current only exists with a circuit...



WE now have a new question, and the answer probably has something to do with the Plank Length and possibly the velocity factor.

In any case, and your raising of a transistor makes me wonder what you are actually thinking about. When to apply a voltage to the transistor's base, current flows with only the "delay" that is defined by whatever threshold we arbitrarily settle on. Let's just say the deal is equal to the time it takes for the first electron to move \( ℓ_p \) (1.616255(18)×10−35 m) which would happen in very close to \( 5.39×10^{-44} \) seconds. That would be one Planck Length in one Planck Second.

That current will be flowing to the base, that current is not yet flowing between collector and emitter seems entirely unrelated to the question at hand.

I must admit it is a little bit off-putting to read you saying:



when I believe you haven't presented a cohesive argument for your assertions and you reject—without relevant counterarguments—cogent objections to what you appear to be saying. It comes off as arrogant and insulting to say "you just don't understand" while from this perspective, your assertions don't have logical consistency.

I wish you would reconsider that. At this point, I will retire from the conversation and ignore the thread.
Hey that was always your choice.

But to quote you once:
"Nothing can start when no time has elapsed. Starting means something has happened, when 0 seconds have elapsed nothing has started."

In electrical analysis theory it is described using plus + and minus - signs after a zero 0.
For example:
A switch is closed at t=0. Find the current at time t=0+.
The plus sign indicates an infinitesimally short time, insignificant. So at time t=0 the switch is closed but we have to have some way to indicate what the current at that time will be so we use that sign.
Sometimes we refer to this as the initial current, but there is often also an initial derivative and possibly other initial derivatives. We often have to solve for this and sometimes the current is zero but the first derivative is non zero and that indicates that the current started at the SAME time s the voltage was applied. So we can say something started at t=0 just like in a horse race and this is very common in electrical theory.

So if you need clarification, the voltage is applied at time t=0 what is the current at time t=0+.
It is a very common way to analyze circuits so i cant understand why this seems impossible.

The main idea in physics is not about a transmission line it is about a single solid mass that is pushed by a force. There is no friction. When the force is applied, the mass begins to move and there is absolutely no delay or anything like that. That's the force current analogy.
The way this looks on a graph is the movement a straight line through the origin that has a positive slope.
Even though the graph starts at 0 it still has non zero slope at zero and that means that it started immediately with no delay. Maybe that is the easiest way to describe it.
So there is no cause and effect because they happen simultaneously.

I didnt really say that anyone didnt understand this because they are stupid or anything, but if you read around the web a little you will find various professors that explain this almost the same way. So just because someone doesnt understand something doesnt mean they are stupid or anything like that. We all dont know everything but as we go we learn from others. If you havent learned anything from this then you are not really trying to you have a notion of how things work and you never want to change that.
But dont believe me. Read around the web. If you dont want to be bothered that's up to you i dont want to force anyone to understand this point.

So just to recap, this discussion is not about having a voltage or current on hand and applying it and then saying that "WE DID SOMETHING" so it must be that that caused something else to happen. Nothing like that at all. It's more about what happens at the very instant of application. At the instant of the application of a voltage the charges begin to move, with no delay, and when things happen simultaneously we can not claim cause or effect for either one. That's the point.

Here is an experiment which might help to show this better.
We connect a 6v battery to two resistors in series, one is 2 ohms and the other is 1 ohms.
We know that we see after some time or not that we get 6/3=2 amps.
Now what happens if we suddenly reduce the 2 ohm resistor to 1 ohm. Does it take 2 years for the current to START to change (final will be 3 amps of course). No. Does it take 2 days? No. Does it take 2ms? No. Does it take 2us? No. Does it take 2ps? No. It STARTS to change immediately or if you prefer at t=0+.

If anyone can propose an experiment that defies this i'd be happy to look at it and examine it carefully. I will probably disagree though because i've read much on this and there isnt any proof that there is a de;lay anywhere. Everywhere there is a claim that one comes before the other is based on a misunderstanding of the question which again boils down to someone applying a voltage by hand and thinking that they caused something so the voltage must be doing it all (ha ha). But please read around the web.
 

Thread Starter

MrAl

Joined Jun 17, 2014
11,396
Sorry - but you have quoted me wrong! Where did I use the term "after"?
In contrary - In my post#20 I wrote:
"Additional remark: I think, the title of this thread is somewhat misleading (...which occurs first?):
According to my interpretation, the word "first" does not apply to a timely sequence (delay between some occurences) but to the "cause-and-effect" problem. "


Added (later):
This thread is the follower of the following
https://forum.allaboutcircuits.com/posts/1708446/
in which we have dicussed (among other items) the question if a current could create a voltage (or if a voltage is always necessary for driving a current) .
As we can see - it was YOU (in post #43 of this foregoing thread) who has created this new thread with the wordings " .....occurs first? ".
So - you have invented the timely sequency into the subject of discussion.
Ok no problem, then what is your counter argument then?
If i say that voltage and current occur simultaneously then why do you disagree? Or do you even disagree?
If you are saying cause and effect then you have to show that is true somehow.
 

LvW

Joined Jun 13, 2013
1,752
Ok no problem, then what is your counter argument then?
If i say that voltage and current occur simultaneously then why do you disagree? Or do you even disagree?
If you are saying cause and effect then you have to show that is true somehow.
* Counter argument? Against what?
* I have never expressed my disagreement (against voltage-current appearence simultaneously) - again, you misquote me.
I have said that simultaneously has nothing to do with cause-and-effect (see my mechanicle example).
* What do you want me to show? That the base voltage is the cause of the currents into the transistor?
This was shown and proofed in uncountable contributions.
Or can you explain to me how a current can exist within a conductive material without an E-field (and the corresponding force) which accelerates the electrons?
 

Thread Starter

MrAl

Joined Jun 17, 2014
11,396
* Counter argument? Against what?
* I have never expressed my disagreement (against voltage-current appearence simultaneously) - again, you misquote me.
I have said that simultaneously has nothing to do with cause-and-effect (see my mechanicle example).
* What do you want me to show? That the base voltage is the cause of the currents into the transistor?
This was shown and proofed in uncountable contributions.
Or can you explain to me how a current can exist within a conductive material without an E-field (and the corresponding force) which accelerates the electrons?
Ok no problem, i guess we just misunderstand each other.

I never said a current can exist in a conductor without voltage except in the case of a superconductor but i dont care to discuss the superconductor view too deeply.

So my view is simply that as soon as a voltage appears a current begins to flow and that's what i call simultaneous.

here is a little graph to illustrate. You can think of this as an inductor if you like.
The voltage is 'applied' at t=0 the far left side with the green circle.
The green circle is where we zoom in repeatedly meaning the time of the gray vertical line changes to smaller and smaller units, ms, then us, then ns, then ps, etc.
We can zoom in forever and we will still see the same graph.

So i assert that voltage and current appear simultaneously and we can not say one 'causes' the other even though it seems like voltage comes first because we happen to be applying that at t=0. It does not matter that voltage seems to 'push' the charges along because the charges only have inertia then dont have any sudden threshold that needs to be reached that starts them moving. That's why i compared the mass and a force because when a mass only has inertia the movement starts immediately just like in that graph. So the force and the movement occur simultaneously.
 

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Thread Starter

MrAl

Joined Jun 17, 2014
11,396
Hello again,

Here are some quotes.

From Wikipedia:
"Force is a useful concept for the explanation of acceleration, but force is not by itself a cause. More is needed."
Then they go on to explain that a CHANGE in force may be REGARDED as a cause, but note the use of the word REGARDED.
They also state that many theories (but not all) requires that the cause precedes the effect, at least temporarily. That is when time data is available.

A quote from an electrical avionics instructor Muralidhar Rao:
"Actually there is no first or second in electricity or electron theory".
Then goes on to explain the balance between a separation of charges and the flow that occurs between them.
Then:
"Therefore i would say that there is no who is FIRST" and the caps are a direct quote also.
Lastly, he compares this to hydrogen and oxygen that form water, and states that if you separate the two you no longer have water (if you separate voltage and current you no longer have energy which means there is no more separation of charges and no current flow.

I think what i learned from the Wikipedia entries was mostly about the word "regarded". We often regard things as being true whether they are or not, as a matter of convenience or even as a matter of survival.
If we are out in the wilderness and we hear a lion's roar, we assume there is a lion we dont assume someone has a tape recorder. If we hear a stampede in the distance we assume horses, not zebras, although ti could very well be zebras. The more common experience dominates our assertion of what might be happening even though it could be something entirely different.

BTW this was originally explained to me back in the 1980's when the chief engineer and owner of the company explained it to me. At first i had a hard time grasping this too because for so long i had used voltage supplies to power circuits and with that there is always the experience that seems to suggest that voltage somehow must come before current. "I applied a voltage and THEN a current began to flow, therefore the act of applying the voltage caused the current to flow". So i REGARDED my application of voltage to be the cause. Looking more closely at what happens, i find out that there can be no delay between the voltage application and current flow.

You will find many references on the web to this kind of experience that tries to suggest that voltage comes first, but they are all based on the common experience not on any scientific data or theory.

Will quantum theory suggest something else? That's a huge question because so much has changed about physics with the study of quantum mechanics. In some specially produced solids it is even stated now that time can flow in reverse. We are really on the edge of new physics and it seems every day some new discovery comes about. Superconducting diodes: a diode that has zero resistance in the forward direction but has finite resistance in the opposite direction. Tiny transistors with superconducting leads that can switch ultra fast. An oscilloscope that can actually see (and plot) the waveform of light itself. Maybe my favorite though is solid state batteries, which are very practical for me because i used batteries for many things and a lot of other people do especially for cell phones and the like.

I guess i will rest my case right there. If this doesnt clear this issue up for you then nothing will.
I may yet still ask a couple friends of mine at MIT though to see how they explain it. Not every PHD works on these things though sometimes they work on more everyday projects.
 

drjohsmith

Joined Dec 13, 2021
852
Guys

An interesting discussion

But

is this not the "chicken or egg first " argument

"Discussion" which has been going on for ever


Personally
Im a simple engineer,
I see both together,
I can not measure one without the other .
 

dcbingaman

Joined Jun 30, 2021
1,065
Consider a 'voltage source'. In order to measure the value of the voltage source, you must pull some current from it. Consider a current source, to measure the current source you must apply a load and measure the voltage across that load. They are two of the same things. A potential difference is created by a current and a current is created by a potential difference. You cannot have one without the other. Some may say you can have a potential difference but that is measured in Joules per C. You cannot have something measured in Joules per C without first allowing energy transfer to occur. Thus neither is 'first or last' they are two sides of technically the same coin. They just appear to us as different when deep down there is no difference between this two things except in practical terms where you want to take advantage of them.
Voltage=Joules/C. You cannot have energy usage per C of charge without C moving from one place to another. Technically a voltage cannot exist without a current flow being present. Some may say that is 'wrong' that a voltage can exist without a current. To which I say. Show me a voltage without a current! You cannot, the moment you go to measure it, you must pull a current, otherwise there is no energy usage per C of charge displaced to even talk about.
 
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sparky 1

Joined Nov 3, 2018
756
A charge on a metal sphere tends to distribute itself evenly.
Another material's composition can have one site holding an isolated charge.
There exists an electromotive force. We know that electric current is the flow of electrons.
The flow condition exist in conductors.

The term Statvolt can better describe the static electrical value.
The conservative electrostatic field that is created by separation of charge
exactly cancels the forces producing the emf. A statvolt can be very large in magnitude.
It would be difficult to study a non-moving charge with a conductive circuit.

Just saying that opposites attract and likes repel does not explain the underlying principle.
The potential and kinetic conversion uses motion which is difficult to disprove.
Quantum mechanics suggests that a photon appears and interacts just as 2 electrons repel.
The sub atomic goes beyond traditional electrical science.
 
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LvW

Joined Jun 13, 2013
1,752
Consider a 'voltage source'. In order to measure the value of the voltage source, you must pull some current from it. Consider a current source, to measure the current source you must apply a load and measure the voltage across that load. They are two of the same things. A potential difference is created by a current and a current is created by a potential difference. You cannot have one without the other.
This sounds a bit too simple,
"Consider a current source..."......So, you automatically assume that there is a real source of current (without a driving voltage).
Please, can you give me one example how a real "current source" looks like?

I know that in electronics we have some circuits called "current source". But dont forget that this is simply a name - nothing else. Its main purpose is to allow a current with is nearly independent on the connected load.
But - physically spoken (and THIS is our subject of discussion, as far as I have understood) - it is a voltage source with (a) a very large constant (ohmic) source resistor or (b) with a dynamic source resistance which can be adapted to the connected load thereby allowing a "constant" current.
Unfortunately, the starter of this thread ("---which occurs first ?") has brought the timely sequence into the discussion ("simultaneousness").
The predecessor of this discussion was primarily about the question "cause and effect".
For my opinion (as I have mentioned before, already) both terms should not be mixed or linked together.
 
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Thread Starter

MrAl

Joined Jun 17, 2014
11,396
Guys

An interesting discussion

But

is this not the "chicken or egg first " argument

"Discussion" which has been going on for ever


Personally
Im a simple engineer,
I see both together,
I can not measure one without the other .
+

Hello and thanks for the reply. I'd like to clear a couple things up.

First, it's not an argument it's a discussion about current and voltage and how they behave.
Second, we are not farming chickens we are talking about electrical circuits and behavior.
But if you are saying that we can not determine what comes first, then that is exactly what i am stating here and i'm convinced this is the general scientific view.

The crux to any opinion here or elsewhere on the web is that some people consider physically connecting a battery to a circuit means that current would not have started to flow if the battery was never brought into contact with the circuit. But what i bring up here is not that, it is what happens with the current at the very moment of contact of the battery leads to the circuit. That would mean that all movement on the part of the human has ended and now we look at the microscopic activity of the current which maybe we can describe in terms of electrons.
Another way to look at this is a battery is connected to a circuit but does not activate anything because there is a power switch that is 'off' at the moment. Then later, a computer closes the switch at t=0. What happens to the current at t=0 or if you prefer what happens at t=0+.
So it has nothing to do with connecting a battery to a circuit really.

An analogy was formed using a force and a mass. As soon as the force begins to push on the mass, the mass beings to move. That's because there is only inertia and inertia is not the same as a resistance.

Also, the discussion started on Wednesday it is now Monday. That is hardly "forever". People like to express their opinions about this because it's an interesting look at electrical principles. Some discussions in science go on for 100's of years before a resolution is found.
 

Thread Starter

MrAl

Joined Jun 17, 2014
11,396
Very well! If I may end this argument. The chicken came first.
Ha ha, thanks for that bit of humor.

I guess if we really wanted to know this we'd have to go back to the 'big bang' or whatever the current theory of the universe is now (it has changed somewhat recently). I guess it would have to do with how charges were first formed in the universe.
As to circuit theory though, there is no way to tell which came first and that is what i am asserting here. The exact experiment here has to be understood first though because it is very specific view of what happens.
 

Thread Starter

MrAl

Joined Jun 17, 2014
11,396
Consider a 'voltage source'. In order to measure the value of the voltage source, you must pull some current from it. Consider a current source, to measure the current source you must apply a load and measure the voltage across that load. They are two of the same things. A potential difference is created by a current and a current is created by a potential difference. You cannot have one without the other. Some may say you can have a potential difference but that is measured in Joules per C. You cannot have something measured in Joules per C without first allowing energy transfer to occur. Thus neither is 'first or last' they are two sides of technically the same coin. They just appear to us as different when deep down there is no difference between this two things except in practical terms where you want to take advantage of them.
Voltage=Joules/C. You cannot have energy usage per C of charge without C moving from one place to another. Technically a voltage cannot exist without a current flow being present. Some may say that is 'wrong' that a voltage can exist without a current. To which I say. Show me a voltage without a current! You cannot, the moment you go to measure it, you must pull a current, otherwise there is no energy usage per C of charge displaced to even talk about.
Although that is still the 'experiential' view that is perhaps a good way to state this.
If you have a voltage source it appears to be one way, but if you have a current source it appears to be another way. If we look at the microscopic view, as soon as a switch is closed current begins to flow regardless if it is from a current source or a voltage source powering the circuit.,
 

Thread Starter

MrAl

Joined Jun 17, 2014
11,396
Electroscope?

There is a momentary movement of charge, but that is not the principal the device works upon, there is no current during the measurement. (other than leakage)
It's interesting that Fluke now has a meter that can measure voltage outside of the wire by measuring the ELECTRIC field. Measuring current outside the wire has been done for ages now by measuring the magnetic field. Now the electric field is being measured in order to determine the voltage.
Since energy is transferred via the two fields and the two fields MUST both be there to transfer energy, they both must occur or start to occur at the same time.
 

LvW

Joined Jun 13, 2013
1,752
First, it's not an argument it's a discussion about current and voltage and how they behave.
Second, we are not farming chickens we are talking about electrical circuits and behavior.
But if you are saying that we can not determine what comes first, then that is exactly what i am stating here and i'm convinced this is the general scientific view.
Yes, I can agree to everything (provided that the term "first" has a purely time-related meaning and does not yet say anything about cause and effect).

@ drjohsmithIt: This is certainly not a "chicken-and-egg" problem. (I must admit that to me it sounds a bit helpless when somebody has no other explanation).
 
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Thread Starter

MrAl

Joined Jun 17, 2014
11,396
A charge on a metal sphere tends to distribute itself evenly.
Another material's composition can have one site holding an isolated charge.
There exists an electromotive force. We know that electric current is the flow of electrons.
Since this condition does not exist with conductors the term Statvolt can better describe
the static electrical value. The conservative electrostatic field created by separation of charge
exactly cancels the forces producing the emf. A statvolt can be very large in magnitude.
It would be difficult to study a non-moving charge with a conductive circuit.

Just saying that opposites attract and likes repel does not explain the underlying principle.
The potential and kinetic conversion uses motion which is difficult to disprove.
Quantum mechanics suggests that a photon appears and interacts just as 2 electrons repel.
The sub atomic goes beyond traditional electrical science.
Hi,

I am not entirely sure i understand your post 100 percent, but i also think quantum mechanics may have something to say about this. In fact, some superconductors can be explained via entanglement (or the lack of it). How that affects the current at the very startup through i have a feeling it doesnt matter unless of course the Poynting vector calculation is somehow found to be lacking. I will look into this shortly just to see if anything new has come about.
 

drjohsmith

Joined Dec 13, 2021
852
+

Hello and thanks for the reply. I'd like to clear a couple things up.

First, it's not an argument it's a discussion about current and voltage and how they behave.
Second, we are not farming chickens we are talking about electrical circuits and behavior.
But if you are saying that we can not determine what comes first, then that is exactly what i am stating here and i'm convinced this is the general scientific view.

The crux to any opinion here or elsewhere on the web is that some people consider physically connecting a battery to a circuit means that current would not have started to flow if the battery was never brought into contact with the circuit. But what i bring up here is not that, it is what happens with the current at the very moment of contact of the battery leads to the circuit. That would mean that all movement on the part of the human has ended and now we look at the microscopic activity of the current which maybe we can describe in terms of electrons.
Another way to look at this is a battery is connected to a circuit but does not activate anything because there is a power switch that is 'off' at the moment. Then later, a computer closes the switch at t=0. What happens to the current at t=0 or if you prefer what happens at t=0+.
So it has nothing to do with connecting a battery to a circuit really.

An analogy was formed using a force and a mass. As soon as the force begins to push on the mass, the mass beings to move. That's because there is only inertia and inertia is not the same as a resistance.

Also, the discussion started on Wednesday it is now Monday. That is hardly "forever". People like to express their opinions about this because it's an interesting look at electrical principles. Some discussions in science go on for 100's of years before a resolution is found.
no problem
 

dcbingaman

Joined Jun 30, 2021
1,065
This sounds a bit too simple,
"Consider a current source..."......So, you automatically assume that there is a real source of current (without a driving voltage).
Please, can you give me one example how a real "current source" looks like?

I know that in electronics we have some circuits called "current source". But dont forget that this is simply a name - nothing else. Its main purpose is to allow a current with is nearly independent on the connected load.
But - physically spoken (and THIS is our subject of discussion, as far as I have understood) - it is a voltage source with (a) a very large constant (ohmic) source resistor or (b) with a dynamic source resistance which can be adapted to the connected load thereby allowing a "constant" current.
Unfortunately, the starter of this thread ("---which occurs first ?") has brought the timely sequence into the discussion ("simultaneousness").
The predecessor of this discussion was primarily about the question "cause and effect".
For my opinion (as I have mentioned before, already) both terms should not be mixed or linked together.
You bring up a good point. You cannot have a current source without a driving voltage and vise-versa. The terms are just approximations used in Engineering. If we have a source of energy connected to a load and the load resistance changes, if the current changes significantly compared to the voltage we have a 'voltage' source. If the voltage changes significantly compared to the current we have a 'current' source. But naturally there is no perfect voltage or current source, thus in reality both voltage and current 'sources' are actually a mixture of the two.
A bench top power supply with current limiting can be thought of as a voltage source, (when the current is below the set limit) or as a current source (when the current is above the set limit). I have used bench power supplies for both scenarios. So here we have something that can be either pending how you use it.
 
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