Talk:Kirchhoff's circuit laws

message: 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)
thread_title:  This article needs some work 

message: 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  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)
replies: text: 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)
replies: text:   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)

text: I agree that the figure could be improved.  Perhaps  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)
replies: text:   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)
replies: text: 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)
thread_title:  Image of KVL is incomplete 

message: Which statement describes cybersecurity? 2401:4900:3133:3E98:0:57:4BCC:BD01 (talk) 14:36, 23 September 2022 (UTC)
replies: text: You are thinking of Kerckhoffs's principle which is completely unrelated. Jonathan A Jones (talk) 16:06, 23 September 2022 (UTC)
thread_title:  Which statement describes cybersecurity? 

message: February 29, 2024
Concerning treatment of Kirchhoff’s Current Law
Dear Editors,
There is a serious problem with the Wikipedia Article on Kirchhoff’s Current Law (viewed February 29, 2024) that directly affects readers interested in modern circuits.
The law is not derived in a way that can be applied to modern circuits. The law is presented as an approximation for slow systems, but modern circuits are not slow.
Here is the formal argument
The current in the discussion of Kirchhoff’s law is the flux of charges with mass.
Kirchhoff’s law then says that charges do not accumulate.
However, the Maxwell Ampere law of electrodynamics says otherwise.
 Take the divergence of both sides of the Maxwell Ampere Law, remember that the divergence of curl is zero (as long as the operators are defined), and see that the divergence of conduction current is NOT zero
Thus, the Maxwell Ampere Law says conduction current DOES accumulate.
Kirchhoff’s Current Law says conduction current does NOT accumulate.
Experiments (e.g., with any circuit of 1 megohm resistors) show transients of the order of 0.1 to 1 microseconds. These transients settle down but on a time scale very much slower than those of modern circuits.
Engineers deal with these contradictions by changing the circuit they are analyzing. They add supplemental elements to the circuit [1-3] creating a new supplemented circuit. They place parasitic (stray) capacitances in parallel with circuit elements. This is the approach in modern design texts [3-10].
This fix-up works remarkably well [10-13], for reasons derived in [14] but the fix-up is not complete, and in that sense, is not correct. The values of the capacitances are unspecified and the large numbers of capacitors needed in modern high speed circuits is problematic, and probably unable to deal with all the time dependence that occurs in real circuits.
Maxwell resolved this paradox by defining a true current that includes a time derivative terms, as does the right hand side of the Maxwell Ampere Law, as discussed at length [14].
Maxwell said (in slight paraphrase) that analysis must include a time derivative term. The logical implication is that analysis without the time derivative term is incorrect. Kirchhoff’s law is thus incorrect in his view.
Whatever one’s view of Maxwell’s comments, the argument in this note is based only on mathematics.
My Request:
Please correct the Wikipedia entry on the Kirchhoff current law so
a)      It includes a derivation of Kirchhoff’s law that is useful on the time scale of modern applications.
b)      The current law is not in conflict with the Maxwell Ampere Law
c)      The derivation and discussion does not confuse students who observe transients in circuits made of only resistors, when Kirchhoff’s law says there should be none.
Reference should be made to the literature with [15] and [16] and moving to the more complete review [14]. My knowledge of that literature is foreshortened by human prejudice and further references should be provided.
Ever yours,
Bob Eisenberg
 
References
1.           Horowitz, P. and W. Hill, The Art of Electronics. Third Edition ed. 2015: Cambridge University Press. 1224.
2.           Scherz, P. and S. Monk, Practical electronics for inventors. 2006: McGraw-Hill, Inc. 1056.
3.           Sedra, A.S., et al., Microelectronic Circuits. 2020: Oxford University Press, Incorporated.
4.           Ayers, J.E., Digital Integrated Circuits: Analysis and Design, Second Edition. 2018: CRC Press.
5.           Dobkin, B. and J. Williams, Analog circuit design volume 2: immersion in the black art of analog design. Vol. 2. 2012: Newnes.
6.           Gielen, G. and W.M. Sansen, Symbolic analysis for automated design of analog integrated circuits. Vol. 137. 2012: Springer Science & Business Media.
7.           Gray, P.R., et al., Analysis and Design of Analog Integrated Circuits. 2009: Wiley.
8.           Lienig, J. and J. Scheible, Fundamentals of layout design for electronic circuits. 2020: Springer Nature.
9.           Muller, R.S., M. Chan, and T.I. Kamins, Device Electronics For Integrated Circuits, 3rd Ed. 2003: Wiley India Pvt. Limited.
10.        Okoshi, T., Planar circuits for microwaves and lightwaves. Vol. 18. 2012: Springer Science & Business Media.
11.        Schwierz, F. and J.J. Liou, Modern microwave transistors: theory, design, and performance. 2003: Wiley-Interscience.
12.        Fukunaga, K. and S. Kurahashi. Dielectric properties of printed circuit board insulations at microwaves and millimetre waves. in Electromagnetics in Advanced Applications, 2007. ICEAA 2007. International Conference on. 2007. IEEE.
13.        Mei, K.K. From Kirchoff to Lorentz modifying-circuit theory for microwave and mm-wave structures. in Infrared and Millimeter Waves, 2000. Conference Digest. 2000 25th International Conference on. 2000. IEEE.
14.        Eisenberg, R.S., Maxwell’s True Current. Computation, 2024. 12(2): p. 22.
15.        Eisenberg, B., et al., What Current Flows Through a Resistor? arXiv preprint arXiv:1805.04814, 2018.
16.        Eisenberg, R.S., Kirchhoff's Law can be Exact. arXiv preprint available at https://arxiv.org/abs/1905.13574, 2019. Beisenbe (talk) 14:54, 2 March 2024 (UTC)
thread_title:  Kirchhoff Current Law needs a derivation relevant to modern, high speed applications