Question

in what cases kichorff`s laws are not applicable to dc circuit

Answer 1

ll give u clue.. Mr. Faraday has something to do with it!

Answer 2

Here is one response to a similar question: "Kirchhoff's laws follow from the conservation of charge and energy in a circuit. Neither is violated in non-conservative fields. A circuit description of such a field would merely act like an active source in a circuit, no different from a battery, which also supplies net energy. For the purposes of circuit analysis the source of that net energy is usually irrelevant."

All I can say, and I've said it before, for those who believe there can not be a potential difference at the terminals of a coil, choke, secondary of a transformer, loops etc.(because they are a piece of wire) simply has not had too much experience with such devices. If you grasp one terminal with one hand and the other terminal with the other hand, of an active high voltage transformer secondary (which is a coil of a single wire), it may well be the last lesson of your life about potential difference or EMF or voltage at the ends of loops of wire.

I am inclined to say "Yes" Kirchoff's law applies to DC circuits, as long as you know how to apply the law.

Answer 3

@radar

Kirchoff's law states that in a closed path the sum of emfs and potential differences is zero

or in other words
\[\int\limits_{a}^{a} E.dL = 0\]

which is not true when u have a changing magnetic field.. which is faraday law


there is a big difference between the potential difference in a conservative STATIC field and EMF generated via electromagnetic induction..

ofcourse if you take two points, you can calculate the difference in potential even in induced fields, but this difference in potential is PATH DEPENDENT .. this is even demonstrated by the famous lecture by a retired Professor Walter Lewin, a professor in physics and an astronomer at MIT

where he demonstrates that two voltmeters connected between two points in a circuit.. read different values..
seeing is believing..

Answer 4

and besides..

kirchoffs law is usually AMENDED.. so as to even consider emf due to changing magnetic field.. which is a source.. yes indeed.. but kirchoff didn't know that changing magnetic field is a source of an electric field.. it was faraday who discovered it.. and it was faraday who also showed that this emf = d (phi) over dt

therefore.. the new loop rule is called faraday kirchoff loop rule.. most textbooks just omit this .. but if u really wanna go according to the history .. then thats the way its done.. ! :P

Answer 5

@Mashy Thanks, I have seen the amended version and almost understand it, but for the DC circuits as posed by the question, how long does this "changing magnetic field" exists? Other than initiaL transient at turn-on or turn-off, where is the changing magnetic field coming from?

Answer 6

well i can always have an oscillating magnetic external field right? :D :D..

Answer 7

but yea.. in real life applications in DC circuits.. its only required in the transient solutions

Answer 8

Oh, O.K. yes indeed, I have seen many of your answers to questions posed here, and I have developed a respect for your knowledge, and have learned some things (even at age 75) lol

Answer 9

oh thank u thank u for ur kind words :D :D

Answer 10

Cheers my friend, I have some chores to do, you have a nice day.

Answer 11

you too :)