Talk:Kirchhoff's circuit laws/Archive 1

Archive 1

copyright notices on images

the copyright notices on the images detract from the professional look of the article. Why not remove its presumably that is allowable under the terms of the GFDL under which it is licensed.--86.17.153.108 16:42, 21 July 2006 (UTC)

Untitled

uhh. wow physics is great, but whatever happened to Es = Er1 = Er2 = Er3 where total voltage equals the same voltage across all branches of a parallel circuit. Why must you make this all greek like?

KVL isn't really talking about parallel circuits, but any closed loop.Alhead 06:22, 20 September 2007 (UTC)

Figure on the Current Law

I think the figure on the Current Law is a bit confusing, because current at the voltage source should be the other way around to be positive.

Or does this have a specific meaning?

sdschulze (talk) 20:51, 11 July 2008 (UTC)

Alhead (talk) 15:54, 28 August 2008 (UTC)The arrows for currents and the pluses and minuses for voltages are simply for reference. In the figure for KCL, any of the drawn voltages or currents could be drawn in the opposite direction. For example, say that the source vg = 5 Volts. If we wanted to, we could draw the same source with the plus and minus exchanged with the new vg = -5 Volts. Similarly, we could draw a new current (call it i5) next to i2, but pointing in the opposite direction. In this case, i5 would be equal in magnitude but opposite in sign with i2. If i2 is 5 amps, i5 would be -5 amps. Does that help answer your question? If the current were drawn the other way, the equation would have to be i1 = i2 + i3 + i4 Alhead (talk) 15:54, 28 August 2008 (UTC)

Original publication?

There is no reference to the original publication of Kirchhoff? When exactly was it published and where? Book, article? -- 89.247.15.158 (talk) 16:35, 11 December 2008 (UTC)

Voltage around a loop

I think the two laws/rules for electrical are not separable. I think that summing the voltages around a loop equals zero is ok because it is one of the principles that defines or proves the current as being in a loop. I prefer to tell students that the summ of the voltage drops around a loop will equal the magnitude of the voltage supplied. Which in the context of a technician is a little more practical Frankenstien 23:49, 11 November 2006 (UTC)

Current doesn't travel in loops, it only travles in a single direction between nodes. Also, circuit components do not supply voltage. Alhead (talk) 15:45, 28 August 2008 (UTC)

Voltage drops are not supplies! I prefer to use mesh analysis when possible.Frankenstien (talk) 05:36, 8 October 2009 (UTC)

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Nice createt Articel.

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Simplification of KVL discussion for a general audience

Hi ! I hope nobody minds, but I have simplified the discussion of KVL, so that (hopefully) it is slightly more suitable for a general audience. If anybody thinks that it is important to discuss detailed issues relating to electromagnetic induction in this article, perhaps they could add a further section. (RGForbes (talk) 19:50, 14 April 2009 (UTC))(Richard)

I think I called it "mangled" as opposed to "simplified", in my edit summary when I reverted it. You wrote "The directed sum of the voltage drops around any closed circuit is equal to the sum of the voltages generated by any voltage sources associated with the circuit." What the heck is that supposed to mean? What's wrong with equal to zero? What's a voltage source "associated with" the circuit? Dicklyon (talk) 04:24, 15 April 2009 (UTC)

hey hi this is mitsul and am just a student studying science. i have a doubt that if there is a resistance in the loop then how does the current remains the same even when the current leaves the loop? please if there is someone who can clear my doubt then it will be very helpful. —Preceding unsigned comment added by Mitsul.kacharia (talk • contribs) 17:03, 17 April 2010 (UTC)

Should we mention transmission line where laws do not apply?

Should we mention the cases where the laws are not valid, as they are superseded by more general application of Maxwell's laws? One example is a transmission line at a high enough frequency. As the article stands, it leaves the impression that the laws are valid for any circuit. elpincha (talk) 20:44, 30 July 2010 (UTC)

Following sources like this one, it would be good to at least point out that what the laws apply to are lumped circuits (see Lumped element model). Dicklyon (talk) 22:33, 30 July 2010 (UTC)

Electric Field and Electric Potential

I believe the article defines the electric potential incorrectly. The electric potential drop between two points is NOT defined as the line integral of the electric field between those two points. This is only true in electrostatics. The electric (scalar) potential V and the vector potential A are defined as scalar and vector fields which satisfy the conditions:

∇×A = B   and    -∇ V - dA/dt = E

These are both ALWAYS well-defined quantities, even if the electric field has non-zero curl.

Instead of stating that the electric potential is not always well-defined, the article should state that the electric field in the circuit is not always completely determined by the electric potential alone. I haven't edited a page before. Before I do, does anyone agree / disagree? —Preceding unsigned comment added by Moderatemax1 (talk • contribs) 00:02, 26 August 2010 (UTC)

Kirchhoff's voltage law assumes that the electric field present is and only is the field present in the circuit. Any electric field external to the circuit, be it conservative or non-conservative, is going to screw up the relationships.Kmarinas86 ^(6sin8karma) 19:02, 26 August 2010 (UTC)

Limitations

the restriction regarding the "capacitor plate"

What restriction? I don't see this mentioned anywhere.

"This is a simplification of Faraday's law of induction for the special case where there is no fluctuating magnetic field linking the closed loop. Therefore, it practically suffices for explaining circuits containing only resistors and capacitors."

So should there be a "limitations" section for KCL also? Generally a limitation to one should have a dual limitation in the other, no? Is this the same as the capacitor plate limitation, or different? —Preceding unsigned comment added by 96.224.70.38 (talk) 14:27, 26 April 2011 (UTC)

Yes, KVL magnetic flux problems, KCL electric flux problems. I've reworked the section you tagged - what do you think? SpinningSpark 18:44, 26 April 2011 (UTC)

Obfustication

Another important article that has had the basic explanation of what is going on smothered by the mathematics nerds. I have just seen these laws explained to a complete beginner in electronics who wanted to know the WHY of voltages and currents around a circuit. They specifically warned against viewing this article as it undermines basic understanding - the worst possible comment anyone could make about Wikipedia. Their explanations were lucid and technically correct and did not require any mathematical analysis. The technical explanations can remain (although adding links to articles that explain what they mean such as summation would help greatly), but like so many other articles in physics, electronics and mathematics giving primacy to a non-technical explanation accessible to a non-mathematically trained audience is essential. And yes I can understand differential calculus and matrix algebra, but many people cannot.The Yowser (talk) 08:41, 7 September 2011 (UTC)

Wikipedia should not be a text book, but my opinion is that at least parts of an article should be accessible to a beginner in the field. I think many people agree on this, but it may be often harder to write a lucid explanation for the beginner (simplifying without removing or altering the essentials). If you just witnessed such a lucid explanation, I would like to invite you to add it to the article, either through incorporation in the existing text, or as an introductory section. – Danmichaelo (talk) 09:20, 7 September 2011 (UTC)

The Second Law is a myth, a slang

The fact that the so called "second law" is considered a Law is one of the best known anecdotes in elecronics. The second law is nothing more and nothing less than one particular interpretation of purely _arithmetical_ relation. Take a loop (a circuit in this case), assign an arbitrary value to each vertex in the loop (voltage in this case) and then calculate the directed sum of the differences between adjacent vertices in the loop. You will always get 0 as the result. The very same result will be obtained with sheep, apples, dollars or demons at the vertices of the loop (instead of volts). This happens becuase 'a - a' is always 0 regardless of the value of 'a'. If you wan't to call it a "law", you can, but it is still an abstract, purely arithmetical law, which in its essense has absolutely nothing to do with electronics, conservation of energy or something like that. i fully and absolutely agree with you.nature,physics are different from very limited purely human imagination! —Preceding unsigned comment added by 92.106.10.4 (talk) 05:06, 30 September 2009 (UTC)

Referring to the physical interpretation of that arithmetical law as a Second Kirchhoff's Law is popular _slang_ among electronics engineers, but formally it is incorrect to call it a physical law. From the formal point of view, it is OK to refer to it as a _rule_, but not as a "law". And, once again, to say that it follows from the laws of energy conservation makes no sense. What it does follow from are the basic axioms of arithmetics. The latter forms the basis for the formal description of any physical laws and, therefore, _predates_ them, not follows from them.

I beg to differ. Without the laws of energy conservation, one could move around a closed loop and continually build up charge, violating KVL. Saying a-a=0 seems trivial, but knowing a-b=0 when 'a' is known can be very helpful. Alhead 06:20, 20 September 2007 (UTC)

Sorry, but you are wrong. The sum of directed differences around a closed loop is always zero. It doesn't matter what quaintity we are considering. Take a loop of any length, generate random values for every node in the loop and then calculate the sum of directed differneces around it. You will get exactly 0. This is guaranteed by the basic arithmetics and has absolutely no connection to electicity, energy preservation and anything else. This arithmetic rule, once again, predates energy conservation. Under these curcumstanes enery conservation follows from it, not the other way around. In the very same fashion, the line integral of electical field on a closed loop is zero because of Cauchy's integral theorem (or, even simpler, Gradient theorem) and has nothing to do with electricity or energy conservation. —Preceding unsigned comment added by 198.182.56.5 (talk) 23:19, 13 March 2008 (UTC)

Yes, as soon as one has a scalar potential function, the sum of the directed differences around a loop is zero. However, the fact that one has a scalar potential function whose gradient is the electric field, i.e. that the electric field is a conservative vector field, is a consequence of physical laws (Faraday's law in the electrostatic case). In fact, in the non-static case (where one has time-varying magnetic fields), this is not true and one does not have a conservative field or a scalar potential energy (energy is being exchanged with the electromagnetic field); in this case, KVL only holds because an "artificial" correction term (the "emf" from inductance) is added. —Steven G. Johnson (talk) 01:43, 14 March 2008 (UTC)

So what? The KVL in its original form is only applicable to scalar potential. This is a required pre-condition for KVL. As you said yourself, KVL has to be modified from its original form in order to work for non-scalar potential. The origional KVL, once again, is a purely abstract arithmetic/mathematical relationship (in both its discrete and integral forms). Its does agree with the principle of energy conservation (it would be strange if it didn't), but stating that it somehow follows from that principle is a major error.

For infinitesimally thin wires (i.e. for circuits), you don't need a scalar potential to express KVL, since you have a specific path of integration of electric field and can therefore define potential drops by $\int \mathbf {E} \cdot d\mathbf {s}$. In this point of view, the fact that the line integral around a loop is zero is not automatic, it is a consequence of the conservative properties of the electric field in the electrostatic case. What these properties are a "consequence" of, in turn, is something of a philosophical issue; one could start with Maxwell's equations etc. and derive conservation of energy, or one could start with the principle of conservation of energy and constrain the form of the static Maxwell equations based on that principle. And then in the non-static case, you have to include a fictitious extra "potential drop" to make it still work...the very fact that the naive formulation of KVL is not always true is an indication of the fact that it is not a mere mathematical tautology, as you seem to think. Anyway, this conversation is a bit pointless, unless you can point to a reputable textbook on electromagnetism that subscribes to your interpretation? —Steven G. Johnson (talk) 03:30, 14 March 2008 (UTC)

Another way of saying it, of course, is that Kirchhoff's voltage law is the statement that one can assign a single-valued scalar "voltage" to each point in the circuit. This is, as you point out, equivalent to the statement that the sum of the voltage drops is zero. But that doesn't mean that there is no physical principle involved—whichever way you state KVL, it is the consequence of the physical properties of the electric field, and those properties are closely related to conservation of energy. —Steven G. Johnson (talk) 05:17, 14 March 2008 (UTC)

No, you get it backwards again. KVL doesn't state that you can assign such a scalar voltage. Because in general case you can't. You described it yourself. Quite the opposite, the original form of KVL requires that such scalar voltages can be meaningfully assigned. This is a required precondition of KVL and under that precondition KVL is automatic. It is ridiculous to even see it debated here. Or see requests for "book references". Any decent book takes the purely mathematical nature of KVL as something well-understood. There's no need for the book to explicitly "subscribe" to that interpretation.

Logical fallacies of similar nature were observed quite a few times already in the history of science. In a well-known example, some psychology researchers concluded that the existence of 6-cliques of friendship or 4-independent sets of animosity in groups of 30-40 students is some psychological phenomenon, while in fact it is an expected consequence of Ramsey's theorem, i.e. a phenomenon of a purely mathematical nature. There's been numerous examples of statistical researchers making incorrect conclusions simply because they fell victim to Monty Hall paradox. And so on. The attempts to claim that KVL derives from conservation of energy is the a fallacy of exactly the same nature. I repeat: KVL in its original ("uncorrected") form is an automatic, purely mathematical relationship. If any of the books you find "reputable" deny this simple fact, you probably have a rather unorthodox criterion of "reputability".

I already explained things clearly above, and you are simply repeating yourself. As I explained, you don't need a scalar potential to express KVL, so a single-valued potential is not a precondition as you seem to think. I'm not going to repeat myself further. The request for references is useful Wikipedia rule that allows me to not bother continuing a pointless debate. —Steven G. Johnson (talk) 00:19, 11 April 2008 (UTC)

No, no, no. I already explained it clearly above. When you started to contradict and correct yourself in your previous (paired) messages, I took it as a sign that you starting to get at least a glimpse of understanding. Now, as you began to contradict the very article your were actually trying to defend, your role in this debate appears to be a simple trolling to me.

I'll return to basics again, for those who get lost in the cloud of useless noise generated here. KVL in its original form is formulated in terms of voltages (potential differences), which are scalar by definition. In this form the KVL is automatic. It agrees with the principle of energy conservation, as everytrhing in physics, but it doesn't follow from it. KVL in its original form (both discrete and integral versions) follows from the laws of aritmetics alone.

As it is correctly stated in the article, it is possible to correct the KVL for the case of "fluctuating magnetic field". This will give you a more general form of closed-llop voltage law, which is often also refereed as KVL, but nevertheless is significantly different form the original KVL.

Voltages are not scalar. Node voltages with respect to ground can be considered scalar, but voltages in the general sense refer to the potential difference at one point with respect to another. Alhead (talk) 15:41, 28 August 2008 (UTC)

I understand the math nerd's distress. KVL seems tautological, because if it didn't hold, then the starting/ending node of the loop in question would simultaneously be at two different voltages (relative to whatever your favourite reference point is). This can't be, hence KVL 'automatically' derives from the definition of a closed loop. And this is the crux of the entire contention b/n the math nerd and Steven Johnson.

What KVL actually states is that a node can have only one voltage (or, more accurately, that a closed loop cannot develop a potential drop across itself). Math nerd takes a node's singular voltage as a given -- as evinced by his suggestion of assigning each vertex in a graph a [single] value -- and is therefore understandably agitated when people claim as a Law the fact that the sum of voltages around a closed loop is zero. (For a more prosaic example, consider a bank account that has a balance of $5 at the beginning and at the end of a month. Obviously, the sum of withdrawals and deposits that occurred during that month is zero.) Dr. Odigitti (talk) 08:19, 27 September 2011 (UTC)

Explanantion of KVL

This law holds true even when resistance (which causes dissipation of energy) is present in a circuit. The validity of this law in this case can be understood if one realizes that a charge in fact doesn't go back to its starting point, due to dissipation of energy. A charge will just terminate at the negative terminal, instead of going on through to the positive terminal.

I have marked this as dubious, although I almost deleted it out of hand along with most of the rest of the explanation. I will put aside the fact the charge carriers are electrons in a circuit and arrive at the positive terminal, not the negative. A generator driving a resistor will constantly drive current through the resistor. The current in the generator winding will be the same magnitude as that in the resistor. It does not just stop on arrival - this would result in an unlimited build up of charge. Pretty sure the same is true of battery cells, only in this case the internal charge transfer is by ion exchange rather than electron flow. If someone can work out what the basic point is here we can copyedit it, otherwise the section is going to get a severe pruning. SpinningSpark 10:55, 11 March 2012 (UTC)

The version prior to this insertion seems to me to be more accurate, as well as clearer and more succint. SpinningSpark 11:23, 11 March 2012 (UTC)

The section is now a lot better, but we still have the recent insertion,

However, if energy is being imparted to the circuit by way of a changing magnetic flux, the induced voltage will not be accounted for by KVL, and a circuit solution based on KVL will not be possible. [2]

The relevant line from the reference for this states'

We'll also postpone a discussion about when Kirchhoff's laws break down for a future article (hint: Faraday's law trumps Kirchhoff's law).

First of all, I respectfully suggest that this citation is nowhere near sufficient to verify the stated claim - it really does not say anything. I agree that the circuital law breaks down in the presence of a changing magnetic field. If we are going to claim that the circuital law is a form of Kirchhoff's law (as our article does) then Kirchhoff's law has indeed broken down. However, has it broken down in the form of sum-of-voltages? This is the form that it is usually given in and understood (and stated by Kirchhoff, and stated in the section the above text is in). Kirchhoff's law as measured by a voltmeter does not break down in the presence of δB. There are numerous books on circuit analysis which apply KVL to circuits containing inductance and transformers. These would all be wrong if that were true. SpinningSpark 11:01, 15 March 2012 (UTC)

Why not antennas?

Another common example is the current in an antenna where current enters the antenna from the transmitter feeder but no current exits from the other end.

This logic can be applied to ANY point on any conductor carrying Alternating Current. If you take any single point along an antenna, the current entering this point will differ from the current leaving it at any instantaneous point of time. The same applies to ANY single point along any conductor carrying AC. If the power station is 1/4 wavelength from the electric stove (a long way but hypothetically), there will be a point in time where the current at the power station is a maximum but at the electric stove zero.

To my mind, Kirchoff's Laws apply equally well to any point on an antenna as they do to any point along a conductor carrying a waveform. To say anything else is to violate the absolute value and nature of the speed of light. One must consider the directed current over a period of time rather than an instantaneous point in time.

Euc (talk) 02:10, 23 May 2012 (UTC)

There is a difference here. If one takes a cut set of a network - a piece of a transmission line say - the sum of the currents entering the terminals of the cut set must sum to zero, just as they do at a node, if radiation is ignored, as it always is in circuit analysis. Remembering that a transmission line consists of two ports, each of two terminals carrying equal and opposite currents, then it is obvious that Kirchhoff's current law is going to apply to the cut set. And if one were to cut through a port so that only one terminal were included then the currents through the transmission line shunt elements would then have to be included as well, again algebraically summing to zero. The situation with the antenna is not the same - a cut set through a piece of the antenna does not have currents summing to zero. The fundamental reason is that radiation is significant and can no longer be ignored. Energy is being radiated away from the antenna. This is similar to energy being dissipated in a resistor, from the point of view of the transmitter, and could be modelled with distributed resistance to ground along the antenna. However, these resistances would be completely fictitious, merely there to model the phenomenon, just as Maxwell's displacement currents which model the same effect, are not real currents. SpinningSpark 22:55, 23 May 2012 (UTC)

No, you completely missed my point. Antennas are no different to any conductor carrying a waveform. It doesn't matter how you cut it. Distributed resistance to ground is also off track otherwise antennas wouldn't work on satellites. No matter what way you look at it, any point in the universe can be considered a node whether along an antenna with currents going in both directions, power going along mains in one direction or internet signals going along the same mains wires in different directions. To say antennas are different because radiation is significant is just missing the point. ALL CURRENT RADIATES and, for other than antennas, small is NOT zero. If you take any point on an antenna or any point on any other conductor carrying a waveform, the current into and out of that single point with differ except for two instantaneous points in time during one cycle. In an antenna, or any ther conductor, if you take any single point and call it a node (or antinode) then sum the currents over one cycle, the result is zero ie. Kirchoff's law holds. — Preceding unsigned comment added by Euc (talk • contribs) 05:48, 25 May 2012 (UTC)

Source? SpinningSpark 10:36, 25 May 2012 (UTC)

Kirchoff's current law applies only at nodes. A distributed circuit like an antenna doesn't have nodes in the sense that circuits of lumped elements do. What is a "single point" on an antenna? If you chop it into small pieces, it's not true that the currents into and out of each small piece are equal, due to distributed capacitance; in the limit, the difference is zero, but that's not KCL. Such a limit law would provide zero help in analyzing an antenna. Dicklyon (talk) 16:35, 25 May 2012 (UTC)

This follows since from that the

I highly doubt this is even proper english, please advice. As a comment, i believe this entire article could be written in plainer english. Are we trying to get as many people as we can into the sciences or are we attempting through some elitist ideology to continue pushing them away ? — Preceding unsigned comment added by Zicada1 (talk • contribs) 22:46, 26 October 2012

"Proper english (sic)": Your title certainly isn't. Specifics of what you are talking about would help. Better still, go improve the article yourself. SpinningSpark 00:43, 27 October 2012 (UTC)

He's talking about the error that came in here. Needs a rewrite. Dicklyon (talk) 02:10, 27 October 2012 (UTC)

Ok, I've cleaned it up and explicitly added the divergence equation (without which it makes no sense unless one already knows the maths - in which case there is no point in reading the article). However, I question whether all that is really needed to explain such a simple concept. Changing charge in a region implies a net current because charge is conserved. That's all there is to it. SpinningSpark 11:52, 27 October 2012 (UTC)

Approximate?

In Jan 2013, this diff by an IP editor redefined Kirchoff's laws to be approximate. I think they are usually taken as "exact" within the "circuits of lumped elements" model (like it says here and here and here and here), in which case they are also essentially exact for AC circuits (up through frequencies where the lumped element model holds). Is there any reasonable basis in sources for this treatment of Kirchoff's laws as approximations? It would seem to be more conventional to discuss the limitations of the model, than to call these laws approximations. Dicklyon (talk) 06:34, 20 January 2014 (UTC)

We get this all other Wikipedia, not just in this article, from physicists denigrating lumped-element circuit analysis. According to them, the field vector representation of electromagnetic laws is the "proper" representation and everything in circuit theory is just an approximation to that. It starts in the Ohm's law article, where it seems to be implied that the non-field form only applies when the field is uniform - obviously untrue, and then permeates through numerous other articles. It might be true that Kirchhoff is an approximation of field theory, but that is not a very useful way of presenting the material to a reader not familiar with higher physics. It is certainly not how these laws were discovered; they all arise out of experimental results, not field-theoretic considerations. Links to field theory articles should be provided, but not made the basis of the article when textbook sources do not take that approach. SpinningSpark 16:17, 20 January 2014 (UTC)

Yes, it tends to be a mess with physicists trying to rewrite electrical engineering. To be fair, the article was not very clear about the applicability of the "laws", so it invited this trouble. Dicklyon (talk) 17:25, 20 January 2014 (UTC)

Ralph Morrison has written a number of books on the subject of grounding and shielding, based on many years of work in the field. Virtually all of this work focuses on situations where Kirchhoff's circuit laws are approximate; otherwise grounding would be a trivial exercise. Morrison has an undergraduate degree in physics, but his graduate degree is in electrical engineering and he is currently a Senior Member of the IEEE, so it would be preposterous to consider him a physics bigot.

It is well known -- and discussed in this wikipedia article -- the approximation can be made better and better by adding imaginary parasitic components to the circuit diagram ... but only at the cost of making the circuit diagram just an approximation to the as-built circuit. The overall effect is to change the nature of the approximation, but the fact remains that some degree of approximation is almost always required, especially when dealing with high precision, high power, and/or high frequency circuits. The fact remains, whenever a changing magnetic field is present, the voltage is not a potential. This is not an opinion; it is an easily observed fact. If you don't believe it, do the experiment. Also note that the existence of transformers, magnetos, and generators (aka dynamos) requires the existence of non-potential voltages. Not to mention radios. Or you could take the theoretical approach; look at the integral form of the Maxwell-Faraday equation long enough to understand what it is saying.

The fact remains, Kirchhoff's laws are approximate. Nothing anybody says on this page is going to change that.

To say the same thing another way: Kirchhoff's law as applied to real circuits is approximate. It might be argued that when applied to the lumped circuit model it is exact ... but that comes to the same thing, since the lumped circuit model is only an approximate model of real circuits.

Jsd 08:59, 24 January 2014 (UTC)

While not disagreeing with the substance of anything you say, it is not really Kirchhoff's laws that are approximate, they are an exact description of the lumped-element model, it is the lumped-element model itself that is an approximation. SpinningSpark 14:33, 24 January 2014 (UTC)

That is a distinction without a difference, as far as the real world is concerned. You can factor it either way:

• A: (Kirchhoff's laws) <-corresponding to-> (lumped circuit) <-NOT corresponding to-> (real world)

• B: (Kirchhoff's laws) <-NOT corresponding to-> (real world)

Either way, there has to be a NOT in there somewhere.

An article that features the first half of statement A to the exclusion of the second half -- and to the exclusion of statement B -- must be considered opinion running roughshod over reality.

The article as it now stands is a quagmire of OR, error, and contradiction. I do not have time to clean up other people's messes.

--Jsd 09:06, 25 January 2014 (UTC)

We cannot directly introduce B×v terms into a circuit representation. We can only represent them with a lumped inductor, and Kirchhoff's rules can deal perfectly with lumped inductors. It's just a pity that such an animal does not exist. SpinningSpark 14:33, 24 January 2014 (UTC)

Actually the required critter does exist. It's called a parasitic mutual inductance ... aka transformer. It is routine to approximate the real-world distributed mutual inductance with a model involving a lumped transformer.

--Jsd 09:06, 25 January 2014 (UTC)

A component which Kirchhoff's laws have no problem incorporating. SpinningSpark 20:16, 25 January 2014 (UTC)

That brings us back to the real issue, namely the aforementioned A/B distnction. It is a distinction without a difference, as far as the real world is concerned.

-- Jsd (talk) 20:40, 25 January 2014 (UTC)

Jsd, the point is that an article on a "law" should be primarily about what the law is, and only secondarily about what it isn't. Morrison is focusing on areas where Kirchoff's laws do not apply, and that's fine. But he's not rewriting Kirchoff's law, or rewriting the WP article on them (and nobody but you used the word bigot with reference to him or any physicist). It is indisputable that Kirchhoff's laws are a pair of equalities. The extent to which those equalities do or do not apply to the real world is what we need to address in the "Limitations" section. Even to real-world EEs, they are treated as equalities when analyzing circuits; external and stray coupling effects are then usually added as variations on the lump-element circuit being modeled, rather than by throwing out the laws. Dicklyon (talk) 04:25, 26 January 2014 (UTC)

Congratulations, you win. Congratulations, you have succeeded in making this article useless for any engineering, scientific, or pedagogical purpose. It's obvious that facts don't matter. I have nothing more to say. Good bye. -- Jsd 05:10, 26 January 2014 (UTC)

The schematic for the KCL is wrong, also this article should be improved more

The current should begin flowing from the positive side of the source, but in that schematic, it flows from negative. Right? ._.

Also the explanations for the laws should be improved and should be more understandable and practical.

--Emreovus33 (talk) 21:34, 19 July 2016 (UTC)

You are talking about the first diagram, right? In circuit analysis, the current arrow directions can be assigned arbitrarily. If the current is actually flowing against the arrow it will be given a negative value. But in actual fact, it is perfectly possible for current to be flowing in towards the positive terminal of a source. It is not possible to say whether this is the case or not in the example because the whole network is not given, only one isolated node. SpinningSpark 23:27, 6 August 2016 (UTC)

It makes sense now. Thanks! Emreovus33 (talk) 00:26, 13 August 2016 (UTC)

This article needs some work

The vector calculus expressions are necessary, but a simpler, more practical explanation of the laws should also be included.

Also the copyright notices on the images are distracting and unnecessary in my opinion. — Preceding unsigned comment added by Rogerbrent (talk • contribs) 18:37, 30 March 2006 (UTC)

Image of KVL is incomplete

To completely specify a current, we must define its reference direction (arrow) and its value or symbol in the circuit diagram. Then, we can apply KCL. This was correctly done in the image of the section "Kirchhoff's current law", which has the caption "The current entering any junction is equal to the current leaving that junction. $i_{2}+i_{3}=i_{1}+i_{4}$".

To completely specify a voltage, we must define its reference polarity (+ and - symbols) and its value or symbol in the circuit diagram. Then, we can apply KVL. However, in the image of the section "Kirchhoff's voltage law", which has the caption "The sum of all the voltages around a loop is equal to zero. $v_{1}+v_{2}+v_{3}+v_{4}=0$", the reference polarities for the voltages weren't specified in the circuit diagram. So such definition of voltages is incomplete. Therefore, the equation $v_{1}+v_{2}+v_{3}+v_{4}=0$ doesn't make sense until we define the reference polarities for the voltages in such image. Please do so, or use another image. It seems Kwinkunks was the user who created the image, so I'd like to ask you to please add the "+" and "-" symbols for each voltage (except for the voltage which is obvious). — Preceding unsigned comment added by Alej27 (talk • contribs) 15:47, 10 January 2022 (UTC)

Those polarities are defined by the currents in each branch. Take a resistor: if you assume that a current is flowing from its terminal A to its terminal B, then terminal A is (must be!) at a higher potential (~voltage) than terminal B. The +/– symbols can be added, but don't need to: if you're traversing a branch of the loop in the direction of the current you take one sign for the voltages, and the other if you're traversing a branch going against the (assumed direction of the) current in the branch. Ponor (talk) 03:57, 11 January 2022 (UTC)

@Ponor: Three things. 1) The branch current isn't even labeled in the figure, nor the direction in which the loop was traveled (recall we can apply KVL without assuming a direction for the current), so there's no way to infer the voltage polarities of the three resistors (sure, we may say the current travels clockwise due to the source, but if I want I can define the positive reference direction for the current to be counterclockwise, and now all the voltage polarities of the resistors in the figure are wrong). 2) If we follow what you say, then the image caption is wrong, the equation should be $v_{4}=v_{1}+v_{2}+v_{3}$ or $v_{1}+v_{2}+v_{3}-v_{4}=0$ or $-v_{1}-v_{2}-v_{3}+v_{4}=0$, not $v_{1}+v_{2}+v_{3}+v_{4}=0$, because the voltages across the resistors are potential drops while the voltage across the source is a potential rise. 3) We shouldn't mix up KVL with Ohm's law; I mean, I understand what you say, but that's true because of Ohm's law, and I believe this article shouldn't bring Ohm's law to the discussion; I can define the polarity for two resistors to be opposite and still get a correct equation from KVL. Thanks for your reply anyway. Let's see what the others think. :) Alej27 (talk) 09:33, 12 January 2022 (UTC)

I agree that the figure could be improved. Perhaps @Kwinkunks: can comment. Anyway, the rule is that as you go around the loop (typically clockwise, but it doesn't matter), you always assign polarities the same way. That is, is you assign + to the first node of the first element that you encounter, then you assign + to the first node of every element as you encounter it. Constant314 (talk) 07:06, 11 January 2022 (UTC)

@Constant314: That's common in mesh analysis, though it's not a necessary rule. We can arbitrarily choose the reference polarities for the voltages of the three resistors, then apply KVL (and later on Ohm's law) and still get a correct result. Because of this, I think we should specify the reference polarity for the three voltages in the figure, and perhaps clarity in the article that they can be arbitrarily chosen. Of course, as you know, once we've arbitrarily chosen the voltage polarities, if we want to apply Ohm's law for a given resistor, the current direction for that resistor is such that the passive sign convention is satisfied in that resistor, so the current direction is not arbitrary if we already chose the voltage polarity; however I believe that should be discussed in the article on Ohm's law, not assumed here. Alej27 (talk) 09:33, 12 January 2022 (UTC)

KVL says that the sum of the voltage drops around a loop adds to zero. For that to work, you must assign the voltage drops as I have outlined. That does not preclude you from assigning other voltages inside the device. In the example, if you went around the loop clockwise, then you would assign the + sign for $v_{4}$ at the bottom of the symbol. If the symbol was a 10 volt source, then $v_{4}=-10$. That is how it must work. If you want to assign arbitrary polarities, then it is a bookkeeping problem. For example, using primes to indicate arbitrarily assigned polarities, you could have $v_{4}^{'}=-v_{4}=10$. Constant314 (talk) 17:03, 12 January 2022 (UTC)