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Blazing goIITian

Joined:	17 Apr 2009
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20 Dec 2009 18:35:33 IST

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RATES ASSURED!!!!!!!!!!! KIRCHOFFS LAW IS NOT VALID IN CHANGING ELECTROMAGNETIC FIELD BUT THEN HOW D

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RATES ASSURED!!!!!!!!!!! KIRCHOFFS LAW IS NOT VALID IN CHANGING ELECTROMAGNETIC FIELD BUT THEN HOW DO WE APPLY IT IN RC CIRCUITS?

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bladeX -rise of a new sun

Blazing goIITian

Joined: 12 Dec 2007

Posts: 1249

20 Dec 2009 20:32:20 IST

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See Kirrchoff's law is valid everywhere ...............contour integral of Econs is 0 everywhere .......on earth as well as in heaven.

YEs the thing is that most people don't know what exactly is the way kirchoff's law applied. Many think that go around the loop and wherever see resistor substract ir and so on. No...........thing is substract or add the cons. electric field.

About your second qs yes in inductor a marvellous thing occurs which i am sorry i cannot explain as that will need nearly 1-2 article. In short when an inductor is charged then changing magnetic field creates a G field or non-cons. electric field.

This prrevent electron from entering the inductor leading to development of charge on the edges of the inductor leading to cons. electric field.

So under steady state force of cons. balances that of non cons. resulting in the eqn that V = -Ldi/dt.

Well hope you must have understood. And really this subject is very interesting if you actually physically feel what is going around else EB will become hell both during JEE as well as in IIT.

bladeX -rise of a new sun

Blazing goIITian

Joined: 12 Dec 2007

Posts: 1249

20 Dec 2009 20:35:43 IST

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if you are not satisfied which you should be as i have not delved into deep explanation ...........you can be precise with your qs so that i can help more

bladeX -rise of a new sun

Blazing goIITian

Joined: 12 Dec 2007

Posts: 1249

20 Dec 2009 20:42:20 IST

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Well i better give one formula else one might be confused.

close integral { Econs. dl } =0..............Kirchoff's law

close integral { Enon-cons . dl } = -d(Flux)/dt ............Maxwell's law

adding them we get

close integral { (Econs + Enon-cons).dl }= -d(Flux)/dt

close integral {E.dl}=-d(Flux)/dt..............final eqn

Note : as D Griffith say : in general Enon-cons should be called as G field but as calling Econs + Enon-cons as E field simplifies matter so

E = Econs + Enon-cons

Hence the last eqn is more imp. as that is sometimes what you apply directly over a loop so that is not 0 but as i call integral Econs =0 as KVL so it remains true everywhere

shashank agarwal

Blazing goIITian

Joined: 25 Jul 2009

Posts: 605

22 Dec 2009 09:09:35 IST

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kirchoff laws are valid EVERYWHERE , ACTUALLY THREE LAWS ( KVL , KCL AND NODAL ANALYSIS ) ARE ULTIMATE . THEY CAN BE APPLIED IN ANY CIRCUIT .NOW AS OF UR QUESTION In short when an inductor is charged then changing magnetic field creates a G field or non-cons. electric field. This prrevent electron from entering the inductor leading to development of charge on the edges of the inductor leading to cons. electric field. So under steady state force of cons. balances that of non cons. resulting in the eqn that V = -Ldi/dt.Well hope you must have understood . IF U HAVE DOUBT ASK

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