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Re: [Phys-L] circuit analysis : a simpler approach?



I was wrong, KL are not universal testing device.

Lets have a batery in a loop with 2 condensers. battery 1.5 V C1=1.5V
C2=0V

Its ok? ...... NO

if the previous conditions were B=1.5V C1=0V C2=1V, when you have a switch
open, and close it


There are several conditions that satisfies KVL, but are not correct. all
VC1+VC2=1.5V


How can you get the correct distribution?

You need another "law" Saravia N1 Law!!!!

In a condenser and voltage source "only" loop, the initial charge
displacement will be 0 in each node.


Saravia N2 will be " in a current source and inductor only cutset, the flux
variation will be the same in all inductors in the set"






2015-09-02 0:27 GMT-03:00 John Denker <jsd@av8n.com>:

On 09/01/2015 06:48 PM, Lulai, Paul wrote:

Wouldnt we get the same result for most dc circuits with resistors and
capacitors in steady state if we worked things by:
A) determining equivalent resistances or capacitances
B) using kirchoffs laws

Here's how I see it:

a) The method of series/parallel reduction is a subset of
Kirchhoff's «laws». In any case where series/parallel
reduction works, direct application of Kirchhoff's «laws»
would have worked also.

b) The converse does not necessarily hold. You can "usually"
do fine with series/parallel reduction, but not always.
Notable exceptions include certain 2D and 3D mesh structures.

c) A mesh of /linear/ elements can be solved fairly
easily, but a mesh with diodes here and there is a mess.

d) There are situations where neither series/parallel
reduction nor Kirchhoff's «laws» make sense. An obvious
example is a big chunk of metal with a current source
at one point and a current sink at another. I suppose
you could model it approximately using Kirchhoff's «laws»
applied to a fine mesh, but I wouldn't recommend it.

e) In cases where series/parallel reduction is a viable
option, I recommend it over other methods. It's quick,
easy, intuitive, and easy to visualize.

Most simple circuits you are likely to encounter fit
into this category, if only because designers don't
like to design stuff that can't be analyzed this way.

As Diego Saravia pointed out, if a solution has been
found by whatever method, you can use Kirchhoff's
«laws» to check it. Verifying a solution is usually
very much easier than deriving it from scratch.

f) What you really need to watch out for are situations
where Kirchhoff's «laws» get the wrong answer (and
series/parallel reduction gets the same wrong answer
for the same reasons). That's because Kirchhoff's «laws»
are predicated on a whole bunch of assumptions that are
not always true in real life. Ground loops are the
canonical example of this.

https://www.av8n.com/physics/kirchhoff-circuit-laws.htm


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--
Diego Saravia
Diego.Saravia@gmail.com
NO FUNCIONA->dsa@unsa.edu.ar

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