Inductor-Capacitor Circuit: E Field & Differential Equation

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SUMMARY

The discussion centers on the nature of the electric field (E field) in an inductor-capacitor (LC) circuit and the correct formulation of the differential equation governing it. Key references include Griffith's equation \(\epsilon = -L \frac{di}{dt} = \frac{Q}{C}\) and the application of Kirchhoff's second rule. Participants clarify that electromotive force (EMF) is derived from the electric field rather than force, emphasizing the distinction between electrostatics and magnetostatics. The conversation highlights the importance of understanding these concepts for modeling physical circuits effectively.

PREREQUISITES
  • Understanding of inductor-capacitor (LC) circuits
  • Familiarity with Kirchhoff's laws
  • Knowledge of electromotive force (EMF) and its relation to electric fields
  • Basic principles of differential equations in electrical engineering
NEXT STEPS
  • Study the derivation of \(\epsilon = -L \frac{di}{dt}\) in detail
  • Explore the differences between electrostatics and magnetostatics in "Electromagnetic Fields and Energy" by Haus and Melcher
  • Learn about modeling physical circuits using lumped parameter models
  • Investigate the application of Kirchhoff's second rule in complex circuits
USEFUL FOR

Electrical engineers, physics students, and anyone interested in circuit analysis and electromagnetic theory will benefit from this discussion.

atavistic
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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.
 
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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?
 

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