## KVL in Ac circuits

Hello,

Why do we use KVL in Ac circuits ?! or to be more specific is it accurate to use it in Ac circuit , just the same accuracy as using it in Dc ?!

Doesn't the current that pass through the circuit itself make it's own variable magnetic field , which crosses the loop of the circle , making ∫E.dl = -d∅/dt , so in the circuit loop we can't say that the field is conservative anymore ?!

also we have the Ac source it self , which functions by rotating into the magnetic field or by applying a time changing magnetic field , so if we expand the circuit diagram and instead of putting the famous "shape" of a sinusoidal voltage source , we but the whole device , we will see also varying magnetic field of another magnitude passing through that part of the circuit

I may think that the second thing I said is already taken into consideration , and that's why we put a voltage source "shape of a sinusoidal voltage source" I just try to get the whole picture .

so , wether we have coils or not in the circuit , doesn't the time-varying current it self make a change to KVL ?!
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 Unfortunately most textbooks rewrite KVL in a form equating to zero. If you use the original form of KVL The sum of the Emfs = The sum of the IR products Then all is well with KVL (poetry) If a magnetic field or other agent injects an EMF into the circuit then that EMF appears on the left hand side of the equation. If that injected EMF is time varying then KVL refers to the instantaneous circuit or to a time averaged set of voltages and currents.
 Recognitions: Gold Member Science Advisor You are right to ask the question as the situation is not as straightforward, as you have shown. However, as long as you are dealing with a circuit in which you can assume 'lumped components' then Kircholff's Second Law can be applied. This works for many many cases of circuit design, for instance when the value marked on the side of a components are what it says and at frequencies where the layout is not critical.

## KVL in Ac circuits

thank you ,

furthermore , about what I said about the time varying current , we know that the (B) resulting from a current loop at the centre = u I / 2R ( providing it's circular) so the ∅ = ∏RuI/2 (( just assuming it is uniform for it will not affect too much)
) and emf = ∏Ru/2 *dI/dt
and to get considerable voltage we need the amplitude of I be a very large number
Does it happen in reality that the ∏*R*Imax equal a large number to make considerable emf ?! ( I don't know what amperes can be used , does any thing use kilo-amperes or mega-amperes in any circuit ?! ( I know ampere it self is a high value and of course that thing will not be a house-machine) .

I just now saw this " conflict :) "