Talk:Kirchhoff's circuit laws

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)

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.

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.

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-loop 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)

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)

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)

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Nice createt Articel.

(coment to coment 1 above:The constant Omega will not remove until the feeld off it will it fall same to 0 as bevor in constants to the Siemens(unit) x,O-Sie....)/Dash not Minos/

Eris Lucan7*/ Su.08.07/19.55 UTC+1

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)

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)