Inductor-Capacitor Circuit: E Field & Differential Equation

  • Thread starter Thread starter atavistic
  • Start date Start date
AI Thread Summary
In an inductor-capacitor circuit, the nature of the electric field driving the current is debated, with discussions on whether it is conservative or non-conservative. The correct setup of the differential equation is questioned, particularly the relationship between EMF (ε), inductance (L), and charge (Q) in the context of Kirchhoff's rules. Clarifications are sought on the derivation of ε = -L di/dt from the integral of the electric field, emphasizing the distinction between electrostatics and magnetostatics. The conversation also touches on the importance of understanding these concepts for modeling physical circuits and electric machines. Overall, the thread highlights the complexities of circuit analysis and the need for clear explanations of foundational principles.
atavistic
Messages
105
Reaction score
0
In an inductor capacitor circuit , what is the kind of E field driving the current? Conservative or non-conservative? And I really don't understand what is the correct way to setup the differential equation for it. This is why:

In high school level textbooks(Resnick Walker), they have applied loop rule.

In Griffith, he says \epsilon = -L di/dt = Q/C

In MIT OCW , walter lewin says \int E.dl = -Ldi/dt = Q/C

I think last two are the same but still can someone clear this.I mean going by what griffith says(hes the best) can someone tell me why is \epsilon = -L di/dt . I know \epsilon = \intf.dl . How can I arrive using \intf.dl that the \epsilon in the circuit is -Ldi/dt. This thing has been bugging me a lot, please reply.

\epsilon = EMF and \int = closed loop integral.
 
Physics news on Phys.org
atavistic said:
I know \epsilon = \intf.dl . How can I arrive using \intf.dl that the \epsilon in the circuit is -Ldi/dt. This thing has been bugging me a lot, please reply.

\epsilon = EMF and \int = closed loop integral.

The e.m.f is not the line integral of force but of the electric field. e.m.f is potential (work/charge) and not energy.

Another thing, it should be EMF=-L di/dt+Q/C (I mean, + rather than = between the last two terms).
It's just Kirchoff second rule: sum of the potential drops equals the EMF.
 
yep, this is getting into my question. there's a pretty good elementary discussion in this
textbook "Electromagnetic Fields and Energy" by Haus and Melcher that gets into the
difference between electrostatics and magnetostartics into the area called {electro-or magneto}
quasistatics, and how to discriminate the difference between the two. I think the differences are
pretty important in the theory of electric machines: rotating magnetic fields and all that. My primary
interest is in modeling physical circuits by extracting lumped models from gemoetric descriptions.
I'll dig out that old textbook and do some reading, maybe we can compare notes?
 
Thread 'Gauss' law seems to imply instantaneous electric field'
Imagine a charged sphere at the origin connected through an open switch to a vertical grounded wire. We wish to find an expression for the horizontal component of the electric field at a distance ##\mathbf{r}## from the sphere as it discharges. By using the Lorenz gauge condition: $$\nabla \cdot \mathbf{A} + \frac{1}{c^2}\frac{\partial \phi}{\partial t}=0\tag{1}$$ we find the following retarded solutions to the Maxwell equations If we assume that...
I passed a motorcycle on the highway going the opposite direction. I know I was doing 125/km/h. I estimated that the frequency of his motor dropped by an entire octave, so that's a doubling of the wavelength. My intuition is telling me that's extremely unlikely. I can't actually calculate how fast he was going with just that information, can I? It seems to me, I have to know the absolute frequency of one of those tones, either shifted up or down or unshifted, yes? I tried to mimic the...
Back
Top