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What are the situations where Kirchoff laws cease to be valid? How we can create circuits based on lumped element discipline, and that can work in real life? We take ideal conditions, but they just are not like that in real life.

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  • \$\begingroup\$ There are none the KCL and KVL are always valid. "We take ideal conditions, but they just are not like that in real life" Agreed but show me an example where that would result in KCL or KVL not being valid. \$\endgroup\$ Commented Jan 21, 2016 at 13:03
  • \$\begingroup\$ So with using ideal conditions, we are enough close to real elements and circuits? \$\endgroup\$
    – Junior
    Commented Jan 21, 2016 at 13:04
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    \$\begingroup\$ Well, close enough. I refer you to the 3rd joke on this page: jcdverha.home.xs4all.nl/scijokes/6.html "A mathematician and a physicist agree to a psychological experiment." It is the same with circuits, maybe not ideal but close enough for practical purposes. :-) \$\endgroup\$ Commented Jan 21, 2016 at 13:09
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    \$\begingroup\$ Also KCL is a law which describes conservation of charge, as long as the amount of electrons does not change, then I do not see how the KCL could not be valid. Charge does not appear/disappear by itself. \$\endgroup\$ Commented Jan 21, 2016 at 13:14
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    \$\begingroup\$ Possible duplicate: electronics.stackexchange.com/q/211467/54822 \$\endgroup\$
    – Timo
    Commented Jan 21, 2016 at 14:04

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From the Wikipedia page on Kirchhoff's circuit laws:
"Both of Kirchhoff's laws can be understood as corollaries of the Maxwell equations in the low-frequency limit.
They are accurate for DC circuits, and for AC circuits at frequencies where the wavelengths of electromagnetic radiation are very large compared to the circuits."

This is a first case in which they are not accurate.

From the same page, but in the Limitations section, you can find some more informations, which I will just copy here (KCL and KVL stands for Kirchhoff Current Law and Kirchhoff Voltage Law, respectively):

  • KCL and KVL both depend on the lumped element model being applicable to the circuit in question. When the model is not applicable, the laws do not apply.
  • KCL, in its usual form, is dependent on the assumption that current flows only in conductors, and that whenever current flows into one end of a conductor it immediately flows out the other end.
  • KVL is based on the assumption that there is no fluctuating magnetic field linking the closed loop.

On the wiki page, you can find a lot more examples regarding the cases when they are not valid.
I also suggest you take a look at the Electrical System part on the Lumped element model page on the wiki.

To sum it up: in most practical applications they will never "cease" to be valid. They can just become less accurate in some cases (described extensively in the wiki).

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