Dear Cyril,

There are many thankful efforts from many bright mind colleagues, but allow me to make a simple contribution.

The ohms law is an experimental relationship describing the electrical terminal behavior of one of the basic circuit elements, the resistor. The ohms law describes the macroscopic behavior of the resistor when acted upon by a voltage or a current. It is the ratio of the voltage drop on the resistor to the current passing through it that determines its resistance to the passage of the current.

It is the passage of the current and the movements of the charge carriers in the resistor which find resistance in the material of the resistor.

LET us now go deeper and investigate the conduction mechanism in an ohmic resistor such as metallic wires.

ON applying a voltage V across a circular wire with cross sectional area A and length L , an electric field E=V/L will be established in the wire.Due the electric field a force F will be developed on the the free electrons in the conductor. consequently they will be l accelerated and because of forces, the frictional, forces their velocity will reach a steady state value. These moving electrons with the steady state velocity constitute the measured current in the resistor. We see that the motion of electrons on response due to applied electric field resembles the motion of masses in a frictional medium.

The most basic stimuli is the electric field which is directly associated with a voltage source.The most primitive and common electrical source is the voltage source which is a form of potential energy

The current source as a form of kinetic energy is a normally a secondary source in the sense it is generated by converting the voltage source into current source.

The material response is determined by the so-called velocity-Field relation ship. The slope of this relation at small electric field is the material mobility.

In displaying the I-V characteristic graphically we represent always the voltage by the horizontal axes as the independent parameter and the current as the dependent parameter.

In conclusion the primary source is the voltage source and the current source is normally derived from it. Therefore it is a secondary source.

Considering the basic stimuli the electric field resulting from a voltage source the current in a resistor is caused by this voltage.

I hope i shed some light on such a basic question.

Conventionally, we teach that applying the voltage causes the current to flow, because we first physically connect the battery to the resistor. However, current and voltage are duals, and so on another planet, they might be teaching that the current causes the voltage.

And what does happen when you connect a current source to the resistor? You probably will master some explanations when the current source is built by a voltage source and a resistor connected in series. But what do you explain if it is a true current source without an excitation voltage source inside (e.g., a charged inductor or a photocell)?

Connecting a current source is what the people on that other planet do, where everything they regard as convention is the dual of what we do.

Although voltage and current are related, they are not the same thing. In simple terms, voltage causes current. Given a Voltage (a battery) and a path for the electrons (a wire), current will flow. Given the path, but no Voltage, or Voltage without the path, there will be no current.

My simple undersanding is that electrical current is just one of the common trasnport processes (e.g. mass transfer by diffusion or by pressure, thermal transfer etc.) where you have a field (potential gradient) and a flow of mass or energy. These quantities are related to each other by a linear equation if the gradient is small. In the statistical physics of relaxation phenomena the analogy is even wider (elastic properties, dielectric, magnetic phenomena etc.). As far as I understand always the voltage (field gradient) is the reason. When you are talking about current source, you discuss the way of producing the potential gradient, which can be diverse.

Then how do we explain the situations when the bob of the pendulum rises and the inductor of an LC tank charges the capacitor?

Ohm's law is an approximation of Maxwell's equations, which is valid under the hypothesis that light speed is infinite, so that current in the resistor and voltage across the resistor appear at the same time, irrespective of the length of the resistor.

I don't think this approximation can be used to determine causal relationships.

For my opinion, the main question, which results from the discussion up to now is:

Is there really a true current source (without a driving potential gradient) ?

Thus, I tend to follow G. Banhegyi and his arguments based on a "potential gradient".

Of course, using pencil and paper I always can transfer a real voltage source into a fictitious current source. But my concern was and still is:

Is there a real current source (in hardware), which physically does not resembles a voltage source with an appropriate source resistance? Therefore, my reference to a "potential gradient".

Lutz, why don't you ask a separate question like, "Is there a true current source?" or, "Is there a genuine current source?"

It is interesting also to discuss if the storing (and charged) elements capacitor and inductor can be considered as voltage and current sources.

OK but a (charged) capacitor or supercapacitor is produced by applying voltage gradient (to achieve charge separation). The same is true for an inductor. There you also have a potential gradient within your "current source" which disappears as you discharge the device.

Cyril, with reference to your original question ("...causal relationship...") I think, the answer strongly depends on the answer to the yes/no question if a current can flow even without a driving potential difference. Therefore, I have placed my question within this part of the discussion.

Regards

Lutz

Maxwell would say: yes, in this specific case, t=0, all all ideal, yes...

Einstein would say,however: make this resistive circuit the length from Earth to Jupiter and turn it on. When will current flow? Or voltage happen?

Lao Tse, in time: voltage and current are the very definition of this resistor, now, in existence. It exists as a resistor. Take out whatever, it will change to whatever

Very interesting viewpoints... I adore mental experiments (especially, empathy)...

BTW if we charge a capacitor (black box), can we think of it as of a varying through time resistor?

Dear Cyril, if you think your resistor as a complex impedance or admittance, it will get sadly more clear ( if any human can call a complex number as something clear). From this scope, coming back to the time domain, yes, it varies with time (complex time)... Remember the Vmax sin e^(-jet) from sinusoids? One step further, square waves.... And then impulse ( rise times associated, inc... ) . Lovely theme!

Forgot to add: think the capacitor as a complex resistor (complex impedance). Calculus for resistor, capacitor and inductor are the same there!

No, there is no cause and effect in Ohms Law. The point is that you ave to study a complete network where Ohms law describes each component and Kirchhoff''s laws the network. This it true for linear time invariant systems.

On the other hand in most cases it is easier to comprehend what happens if you consider current being the cause of potential driving it through the component. Just as well other systems are easier understood looking at current as the driver for observed events.

Hi Peter, may I place two comments to your contribution?

1.) For my opinion, you have provided no reasoning for the first claim;

2.) You "consider current being the cause..." and you state that "systems are easier understood looking at current...".

No doubt about this. Of course, very often calculations are simplified if we consider the current as a signal source able to produce a voltage.

However, for my understanding, the original question was if there is a physical causality between voltage and current .

Regards

Lutz

We only observe physics by modeling with math. We will never get closer than our models describe and confirm with experiments. Ohms Law (that the question originates from) is a model not reality. That is why there is a clear answer regarding Ohms Law, No!

Yes, we are creating "models" for physical phenomena.

However, in many (or some?) cases, these models do not reflect pure physical truth but the main purpose is to simplify calculations only.

Example: I remember a very long and detailed discussion elsewhere whether the BJT really is current-controlled. Surprisingly, one can find different explanations in various textbooks regarding this subject.

To further develop the cause and event question I suggest to rewrite the original question to this discussion thread. The reference to Ohms Law should be taken out of the problem statement. This will bring the discussion forward. My experience is that in all electrical (time continuous / linear) examples I have worked on there has been two correct ways to understand and explain them.

Ohm's Law is applicable to the Resitance or Part of the Resistance. The V - I Relationship for Resistance can be expressed either way but there is a constraint to Ohm's Law,that the Ohm's law holds good only when the temperature remains constant.

The Resistane of most of the materials increase with increase in temperature and their Temperature Coefficient of Resistance is Positive.

There are some materials with Negative Temperature Coefficient like Carbon,the resistance of an electric arc and their resistances decrease with increase of temperature. Unfortunately many persons ignore this constraint of Temperature.

Non Linear Resistances are not exactly governed by Ohm's Law.

The voltages across an Inductance or Capacitance do not obey Ohm's Law.

Only in the case of Pure Resistance the current or voltage immediately changes without any Time Delay, with change in Voltage or current, either in D.C. or in A.C. as both will be in phase.

Dr.P.S.

We get addicted to time domain. Lest go Fourier for a while, let's go spectral! You see a sinusoid, Fourier sees a line, pure frequential dc. Ohm s law rules there! The question is deep, multidimensional, ludic. Time goes another direction (and dimension) than V and I. And our brains are not suited for more than two or three axis, depending on the person. To worsen things, time has recently been awarded a complex component... You will kill your pupils!

Johnathan Aspinwall - I strongly support your contribution.

I think, the original question (causal relationship) refers to PHYSICAL explanations only (and not to any model descriptions).

And in this context I like to repeat my previous question: Is there any device which can transfer mechanical, magnetic, optical or any other form of energy DIRECTLY into an electrical current ?

Hi, everybody here!

As I can see, the discussion has become extremely interesting... I would like only to add that, for my humble educational purposes:), it is not so important if there is a causality in Ohm's law; if there is not, I will intentionally introduce it:) Of course, I realize that to think of the humble resistor as of a converter with an input and output whose output quantity comes after the input one is quite artificially. But this approach is extremely useful later, in the area of electronic circuits with negative and positive feedback. It is impossible to consider thoroughly their operation without "seeing the integrator inside the op-amp"; otherwise we fall into a vicious circle traveling the feedback loop:

http://en.wikibooks.org/wiki/Talk:Circuit_Idea/Slowing_Circuit_Processes

To show the basic circuit ideas to my students, I do not present circuits as ready-made circuit solutions. Instead, I build (reinvent) step-by-step circuits; thus all we together, my students and I, follow the circuit evolution through the years. And to be consistent, I start from the very beginning - the elementary Ohm's electrical circuit with its three electrical attributes (V, I and R). I consecutively assign a role of an independent quantity to one of them (supplying the circuit first with a voltage source, then with a current source) and a role of a dependent quantity to the other. Then we begin varying (mentally or really) with the independent and read the dependent quantity to investigate the circuit operation. The results are usually visualized by moving (frequently, animated) IV curves, voltage bars and diagrams, current loops and live analogies on the screen...

What does it mean to make the current play a role of an independent variable? Practically, it means to change the exciting voltage or to add a "helping" voltage to it or to change the resistance so that to set the desired input current... what actually means to produce current (to make a current source) by means of negative feedback. There are also more exotic current-creating techniques without using a negative feedback based on the bootstrapping and negative resistance:

http://www.circuit-fantasia.com/circuit_stories/inventing_circuits/current_source/current_source_philosophy/current_source_philosophy.htm

I would like to thank you for the contribution to this question; I was especially impressed by these brilliant thoughts:

Gyorgy: "...My simple undersanding is that electrical current is just one of the common trasnport processes (e.g. mass transfer by diffusion or by pressure, thermal transfer etc.) where you have a field (potential gradient) and a flow of mass or energy..."

About your thought "...OK but a (charged) capacitor or supercapacitor is produced by applying voltage gradient (to achieve charge separation). The same is true for an inductor. There you also have a potential gradient within your "current source" which disappears as you discharge the device...", I would like to note that in the inductor example the two phases - charging (applying a voltage) and discharging (producing a current), are separated in time. So, in the second phase, there is no voltage inside the inductor...

Peter: "...in most cases it is easier to comprehend what happens if you consider current being the cause of potential driving it through the component. Just as well other systems are easier understood looking at current as the driver for observed events..." and "...in many (or some?) cases, these models do not reflect pure physical truth but the main purpose is to simplify calculations only..."

Lutz: "...Of course, using pencil and paper I always can transfer a real voltage source into a fictitious current source. But my concern was and still is: Is there a real current source (in hardware), which physically does not resembles a voltage source with an appropriate source resistance...?" and then, "I think, the original question (causal relationship) refers to PHYSICAL explanations only (and not to any model descriptions)..."

About your thought, "I remember a very long and detailed discussion elsewhere whether the BJT really is current-controlled", it is extremely interesting to discuss this question. Two weeks ago, I invited Rakesh Prabhakara to ask this question and to present his intriguing "theatre play":

http://analogisfun.wordpress.com/2012/04/05/clash-of-the-analog-chefs/

Mario: Your thoughts are extremely interesting and extraordinary... About "We get addicted to time domain" I would say that I stay there since (IMO) the time domain is the most suitable place for my intuitive thinking and imagination. The instant quantity is the only real quantity; the other representations are less or more "integrative" and artificial, and prevent the intuitive understanding. An example: there is only one real thing existing on the screen in the present moment - a little spot; the other pixels are imaginary...

Johnathan: "...Most of what you're using with Ohm's law, as others were noting, is a model that can be used to analyze the circuit, but if you're really looking for a causality in Ohm's law, you need to go back to the basics and study the fundamentals of what is PHYSICALLY actually creating the current, and PHYSICALLY what is creating the voltage..." and also, "...if you're looking for the time delay, we just may not be able to see it with our instruments today (that propogation may be close to the speed of light)..."

Regards, Cyril

Dear Cyril,

There are many thankful efforts from many bright mind colleagues, but allow me to make a simple contribution.

The ohms law is an experimental relationship describing the electrical terminal behavior of one of the basic circuit elements, the resistor. The ohms law describes the macroscopic behavior of the resistor when acted upon by a voltage or a current. It is the ratio of the voltage drop on the resistor to the current passing through it that determines its resistance to the passage of the current.

It is the passage of the current and the movements of the charge carriers in the resistor which find resistance in the material of the resistor.

LET us now go deeper and investigate the conduction mechanism in an ohmic resistor such as metallic wires.

ON applying a voltage V across a circular wire with cross sectional area A and length L , an electric field E=V/L will be established in the wire.Due the electric field a force F will be developed on the the free electrons in the conductor. consequently they will be l accelerated and because of forces, the frictional, forces their velocity will reach a steady state value. These moving electrons with the steady state velocity constitute the measured current in the resistor. We see that the motion of electrons on response due to applied electric field resembles the motion of masses in a frictional medium.

The most basic stimuli is the electric field which is directly associated with a voltage source.The most primitive and common electrical source is the voltage source which is a form of potential energy

The current source as a form of kinetic energy is a normally a secondary source in the sense it is generated by converting the voltage source into current source.

The material response is determined by the so-called velocity-Field relation ship. The slope of this relation at small electric field is the material mobility.

In displaying the I-V characteristic graphically we represent always the voltage by the horizontal axes as the independent parameter and the current as the dependent parameter.

In conclusion the primary source is the voltage source and the current source is normally derived from it. Therefore it is a secondary source.

Considering the basic stimuli the electric field resulting from a voltage source the current in a resistor is caused by this voltage.

I hope i shed some light on such a basic question.

Prof. A. Zekry,

thank you for this contribution.

I think it answers my former question ("Is there any device which can transfer mechanical, magnetic, optical or any other form of energy DIRECTLY into an electrical current ?").

Regards

LvW

The distinction trying to be made by Abdelhalim Zekry as to which is primary, Voltage source or current source is a matter of Perception. Any of the two can be treated as Primary and the other as secondary , I feel considering the property of the Energy Sources.

We know that any Resistance in parallel with a Voltage Source is Redundant element, because even if that Resistance is removed,the Voltage across those two terminals will be the same as the voltage of the Voltage Source. Hence only the Resistance in Series with the Voltage Source causes the voltage drop across it and is Governed by Ohm's Law. Then we can say that the Voltage Source is Primary.The Internal Resistance or Source Resistance of Voltage Source is negligible and the same Current flows inside the Voltage Source.

Any Resistance in series with a Current Source is a Redundant Element since the same current of the Current Source will be pushed through that Resistance.

Only in the case if that Resistance is in Parallel with the Current Source then a part of the current supplied by the Current Source will pass through that resistance and only the remaining current will be supplied to the Load Resistance connected across the Current Source. Then Current Source is Primary.

The Source Resistance of the Current Source ( in Parallel) is Very High.

When calculating the Load Current supplied by a Current Source we use the Parallel Current Distribution Theorem

Refer Thevenin's and Norton's Equivalent Circuits.In Norton's Theorem.

In the case of Norton's Theorem we use the other form of Ohm's Law ( I = V / R )

Then Current Source is Primary.

Dr.P.S.

We should remember that Ohm's law is a simplification, linearization and a discretization of a much more complicated physics problem. The relationship expressed is between potential and kinetic energy, the relationship doesn't exist without both.

You step on your tongue, if you confuse language and mathematics for the physical world being described.

"Then Current Source is Primary."

Yes, we TREAT such a (artificial?) current source as primary.

But does a current source physically exist?

James, would you explain what the idiom "step on your tongue" means?

Abdelhalim, you have exposed in a very persuasive manner your viewpoint. I consider you as an erudite in this field. In addition, you have the gift to explain things in an encyclopedic manner looking from a neutral point of view what is the main idea of Wikipedia contribution. Have you tried to contribute the world encyclopedia?

Pisupati, I have read with pleasure your exciting essay about the two sides of the same electrical phenomenon. How beautifully you have said it in this, symmetrical and reversible, story about Thevenin's and Norton's ideas...

As I can see, we share the same educational idea - that it is not so important if there is really a true current source and if there is really a causality in Ohm's law. We need them for the purposes of understanding and we intentionally introduce them...

Regards, Cyril.

In accordance with the Lutz's persisting question, "But does a current source physically exist?", I am also waiting for an answer to my question, "Is the charged inductor a true current source?" To help the answering, here is again a link to the Wikibooks story about the LC tank where the two storing elements (an inductor and capacitor) alternatively act as sources:

http://en.wikibooks.org/wiki/Circuit_Idea/How_do_We_Create_Sinusoidal_Oscillations%3F#Initial_steady_quantity

I would like to ask the simple question, "What is a charged flywheel putting in motion a car?"

http://en.wikipedia.org/wiki/Flywheel_energy_storage

.

Oh dear.

.

The above (long) thread suggests

that the basic training of teachers

(and others) in the "fundaments" of

our profession is seriously in doubt.

.

Do we really have any doubts about

what is the prime cause and what is

a consequence of that force?

.

Voltage is a form of energy and thus

primal. Current is a numerical count

of charge packets moved by applied

energy. It is thus consequential.

.

The Lone Arrange

Dear Barrie Gilbert,

I have no doubt that the voltage is what determines the current... and I constantly use this fact... including today's laboratory exercise on semiconductor devices...

But in some examples of "current sources" (charged inductor, current circulating through a superconductive loop, nonelectrical - charged flywheel putting in motion a car...) it is not clear where the internal exciting voltage is...

It seems, in the case of the charged inductor, the accumulated magnetic energy is the "voltage"... but what does make the current circulate through the superconductive loop? Maybe a kind of "inertness"... like in the case of the charged flywheel... or a pendulum passing through the zero position?

(Maybe I will have to practice the latter with the cradles of playgrounds... because my little grandson has grown up enough:)

.

Cyril:

.

See -

https://en.wikipedia.org/wiki/Persistent_current#Persistent_currents_in_superconductors

.

The Lone Arranger

Energy is always at the beginning :-)

It is the prime mover.

Interesting... though not so comprehensible for an ordinary person... Maybe Nikolai can help...

I am most impressed by the persistent mode of a superconducting magnet:

https://en.wikipedia.org/wiki/Superconducting_magnet#Persistent_mode

At first glance it seems to be a perpetual motion machine:) ... but then we see that energy is required to maintain the absolute zero temperature...

OK, then let's seek for another reason it not to be a perpetual motion machine:)

Perhaps it is such a machine only until we try to consume energy from it... to load it... as in the case of a freely moving body...

So, if we insert a resistor in the cuperconductive loop, in the first moment, a voltage drop will appears across it... and then both the current and drop will dissappear...

Then the next powerful idea (I name it "artificial superconductance" or "active superconductance":) can help:

We connect an additional voltage source with V = R.I in series with the resistor to compensate the losses in the resistor.

The op-amp in inverting configurations does exactly this work.

I tend to think that there is no causal relationship in general. Note that voltage and current are really approximations of the electric and magnetic fields. In statics, perhaps one can argue that a voltage (electric field) will induce charge particles to move, resulting in a current. But in time-varying situations, Maxwell's equations tell us that electric fields and magnetic fields are coupled with each other. Electric field can "generate" magnetic field (Ampere's law) and magnetic field can "generate" electric field (Farady's law). As such, there doesn't seem to a clear causal relationship between voltage and current.

edit: some minor edits.

Interesting...

Exactly, Nikolai... The world of "currents, voltages, loops and nodes" (i.e., circuitry) has its own laws and techniques of understanding and explanation which are specific and sometimes quite different from those governing in physics.

I think the difference is that physics deals with particular elements while circuitry deals with systems of elements (i.e., circuits).

If the physical dimensions of the circuit are considerably smaller than the wavelength (the shortest), we can use the theory of circuits with lumped parameters. And let's be glad that it is so (easy?) :-))

Dear all of you

Ohm's law expresses a relationship between voltage and current.

We may ask what is voltage and what is current and why do we

use these concepts in connection with electrical circuits.

We deal with electromagnetic field systems.

We believe that Maxwell's equations may be used for modelling of these systems.

That is charge Q and flux FI are used as primary variables.

Charge and flux are difficult to measure so instead we use

the time-derivatives current I=dQ/dt and voltage V=dFI/dt.

As stated by Josef Puncoch'r we assume that our electrical circuits

are quasi-stationary so we may setup lumped element models based on

n-terminal components. Kirchhoff's laws are to be obeyed.

Resistors are current controlled voltage sources.

Input signal current. Output signal voltage.

Conductors are voltage controlled current sources.

Input signal voltage. Output signal current.

Sorry I forgot to ask you what kind of sources are capacitors and coils

Quote:

"Resistors are current controlled voltage sources.

Input signal current. Output signal voltage.

Conductors are voltage controlled current sources.

Input signal voltage. Output signal current."

Hello Erik!

I agree that in our daily practice we can treat the resistors as if they were "voltage sources" (because we can measure the input current as well as the voltage across both ends of the resistor). However, physically spoken, I think this is not correct because - in this view - we assume that there would be a device which really acts as a "current source". But - as discussed here already some time ago - in electronics we cannot realize a real "current source", which would be able to "produce" a voltage. In all these cases, the quantity we call "current" is always the result of a driving voltage.

Again, a "provocation" to conventionally thinking people:)

Erik: "Resistors are current controlled voltage sources." Erik, if resistors were sources, they would solve the energy problems of mankind - by connecting multiple resistors in series, we would make high-voltage batteries and supply our devices:)

Lutz: "... we can treat the resistors as if they were 'voltage sources' (because we can measure the input current as well as the voltage across both ends of the resistor)." Yes, Lutz... but we will be a little puzzled by the reverse direction of the current inside this "source" as it flows from (+) to (-).

Erik: "Conductors are voltage controlled current sources." Erik, I find it difficult to agree with that. How big will the current be? Infinite? Why the simple resistor does not do this donkey work?

Regarding your last question, I think that capacitors and coils are quite more real voltage/current sources than resistors and conductors:)

Hello Lutz,

We use the extended node equations for a first order differential equation model for our lumped element model of an electronic/electrical circuit.

Our primary variables are the node potentials/voltages and the impedance branch currents.

The capacitor is a current source controlled by the time derivative of the voltage

( IC = d(VC)/dt ), ( IC = sC VC = C dVC/dt )

The coil is a voltage source controlled by the time derivative of the current

( VL = d(IL)/dt ), ( VL = sL IL = L dIL/dt )

Concerning:

"""

But - as discussed here already some time ago - in electronics we cannot realize a real "current source"

"""

To me, the Howland Current Source is a real "current source"

http://www.falstad.com/circuit/e-howland.html

http://www.ti.com/lit/an/snoa474a/snoa474a.pdf

http://www.circuit-fantasia.com/circuit_stories/understanding_circuits/current_source/howland_current_source/howland_current_source.htm

https://www.google.cz/search?q=Howland+Current+Source&client=firefox-b&dcr=0&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjfvtiIraPZAhXsYd8KHQA2CSsQ7AkIQQ&biw=1366&bih=693

Erik,

The Howland current source is just an electronic circuit that keeps up a constant current through the load by injecting an additional current (i.e., it consists of a "helping" current source in parallel to an imperfect resistor-type current source).

All sources are only transformers of energy whose origin we do not know :-))

big bang?

God?

Josef

All sources are only transformers of energy whose origin we do not know :-))

big bang?

God?

Josef?

(Josef - you forgot the last question mark)-

:)))

I have rather just consume :-)

Josef

Quote Erik:

The capacitor is a current source controlled by the time derivative of the voltage

( IC = d(VC)/dt ), ( IC = sC VC = C dVC/dt )

The coil is a voltage source controlled by the time derivative of the current

( VL = d(IL)/dt ), ( VL = sL IL = L dIL/dt ).

Erik - I don`t think it is allowed to derive any information about cause and effect (controllability) from a mathematical/physical relationship between two variables.

Example:

Ic=f[exp(Vbe)] physically correct ; effect=f(cause)

Vbe=f[ln(Ic)] physically wrong.

Erik, Happy Valentine's Day:)

Lutz, but for T1 Vbe=f[ln(Ic)] is correct:)

Cyril, I don`t think so - from the physical point of view.

The BJT is a voltage-controlled device - and it cannot change its working principles.

After switch-on of V1 there is a positive voltage at the base of T1 which "opens" the collector-emitter path and allows a collector current Ic1. As a result - the collector voltage drops down until we have a stable DC operating point (equilibrium). As soon as Ic1 is too large, the rising of the voltage drop reduces the base potential and Ic1 will be reduced again. This is a kind of negative feedback (100% feedback between C and B).

Technically and theoretically it is possible to power the base of the transistor from a current source. Now what :-)

Josef - I know that some people are using the term "pumping a current" into the base. However, this may sound "nice" but it is wrong. What is the power behind this "pump"? It is a VOLTAGE! !

And this brings us back to a question we have discussed already: Are there real "current sources"?.

Answer: No, each technical device, which we may call "current source" is, in fact, a voltage source with a sufficiently large source resistor - and the effect of "voltage drop" is nothing else than a special form of "voltage division".

Lutz - Well, I can hardly refute your practical statements. I will think about it :-)

Hello Cyril

Concerning:

---------------

Erik: "Conductors are voltage controlled current sources." Erik, I find it difficult to agree with that. How big will the current be? Infinite? Why the simple resistor does not do this donkey work?

----------------

I = V/R = G*V = G(V) i.e. the current is a function G of the voltage V

V = R*I = R(I) i.e. the voltage is a function R of the current I

It is just a matter of modelling lumped element circuits.

all the best to all of you

ERIK

Erik - can mathematical relations always give reliable information about physical properties (cause and effect, source of voltage or current)?

Regards to you

Erik, are resistors conductors?

.

Fellow Travelers:

.

I find this thread to be a really surprising

indictment of its academic participants.

.

It may be good for maintaining a strong

brain tone to raise at least some of these questions, occasionally, in front of a fine

log fire and in convial company, perhaps

with a good Scotch to oil the wheels. But

it is strange to find statements like this

one: "Conductors are voltage controlled current sources." (They're manifestly not

that, since a current source - by design -

will deliver essentially the same current whatever voltage it happens to generates

in an arbitrary load. It's far more useful to

simply consider the DC resistance of the conductor, or its RF impedance).

.

It's not useful to make claims of this sort

in an environment such as ResearchGate.

This site is intended for the interchange of

help on matters which are puzzling or even

even worrisome to the people who post the

questions, and the clear answers we offer

are (we trust) on-target, authoritative , and

hopefully of lasting value in young careers.

In this case the topic evidently arose in an

attempt to raise a few comments from the academic community, not because of any great personal puzzlement (I hope!).

.

It is understood that to philosophise about

the deep fundamental aspects of a subject

can be very refreshing - in the right place,

and at the right time.

.

The Lone Arranger

... That is why, in 2008, my students and i wrote this popular story about the Ohm's experiment...

https://en.wikibooks.org/wiki/Circuit_Idea/Walking_along_the_Resistive_Film

... where Ohm's law is geometrically presented as a triangle...

Dear Barrie,

the sentence "Conductors are voltage controlled current sources" should be better rephrased as "Conductors are current sources controlled by the voltage at their terminal" this will be correct, but it will be always a trick inside our model. Sometimes during circuit transformations my students obtain current sources controlled by the voltage at their terminal, and they even bother to substitute them with resistor, since at the end all adds up the same.

We are all aware that circuit theory is an approximate model of reality, and that the Ohm's law does not exist in the real world so that someone can say that this discussion is like about which came first, the chicken or the egg.

But, in my opinion it is not a silly thing, when you have a model, trying to see, with all appropriate precautions, what it can tell about the modelled system.

So, if we use incident and reflected waves (a, b parameter) to describe our resistor, we know that a^2-b^2 is the net power entering the bipole, and I hope that we all agree that the reflected power is the effect of an incident power and not that the reflected power is actually causing an incident power. For this reason in S-parameter representation, a is always considered the input and b the output.

Finally, if we write the a, b expressions (R0 is a normalization factor) and our resistor relationship:

a = 0.5(v+ i R0)/sqrt(R0) ;

b = 0.5(v - i R0)/sqrt(R0));

b = a (R-R0)/(R+R0);

we can observe that both voltage and current appear in cause and effect.

greetings

S.

Each source must be able supply energy. Can do it resistor?

Yes, Josef... the resistor could do it... if only it was a negative resistor:)

Dear Lutz, Cyril and Barrie,

Thank you for your comments. Please take a look at Simone's answer.

cite:

- - - the sentence "Conductors are voltage controlled current sources" should be better rephrased as "Conductors are current sources controlled by the voltage at their terminal" this will be correct, but it will be always a trick inside our model. - - -

I use this TRICK to explain the extended node equation modelling of

lumped element circuits with the node potentials and the impedance branch currents as the primary variables.

Modelling is an art

all the best

ERIK

Erik : "lumped element circuits with the node potentials and the impedance branch currents as the primary variables."

i.e. the Modified Nodal Analysis that, as far as I know, is also the circuit solution method used by Spice based solvers.

best regards

S.