Ambiguity of Curl in Maxwell-Faraday Equation

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Discussion Overview

The discussion revolves around the ambiguity of the curl in the Maxwell-Faraday equation, specifically in the context of determining the electric field generated by a changing magnetic field. Participants explore the implications of boundary and initial conditions in solving this problem, with a focus on theoretical and conceptual aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants note that the inverse curl of the right-hand side of the Maxwell-Faraday equation is not injective, leading to multiple potential solutions for the electric field.
  • Others emphasize the importance of boundary and initial conditions in ensuring the uniqueness of solutions in differential equations.
  • A participant suggests a hypothetical scenario involving a circular current loop generating a magnetic field, questioning how to derive the electric field under specific conditions.
  • Another participant argues that the electric field is not uniquely determined by Faraday's Law alone and that both curl and divergence, along with boundary conditions, are necessary to specify a vector field.
  • Some participants express skepticism about the physical realism of the proposed scenarios, questioning whether they violate principles such as energy conservation.
  • There are discussions about the need for boundary conditions, with participants providing examples and debating the adequacy of the specified conditions in the context of the problem.
  • One participant mentions the relevance of the Helmholtz theorem in determining vector fields and stresses the need for a complete set of Maxwell's equations to find correct solutions.

Areas of Agreement / Disagreement

Participants generally agree on the necessity of boundary and initial conditions for solving the problem, but there is disagreement regarding the specific conditions that should be applied and the physical realism of the scenarios being discussed. The discussion remains unresolved with multiple competing views on how to approach the problem.

Contextual Notes

Participants highlight limitations in the problem setup, including the unrealistic nature of the scenarios proposed and the potential for misconceptions arising from traditional approaches to electromagnetic theory. The discussion also reflects a tension between classical and relativistic formulations of electromagnetism.

  • #31
vanhees71 said:
Again, a vector field is only completely specified when giving it's curl and its divergence together with the boundary conditions. Look for Helmholtz's fundamental theorem of vector calculus!
Do you need any clarifications with the notions in #23 and #27? (and I'm not trying to be rhetorically snarky)
 
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  • #32
As I said, I don't see the physics behind your artificial assumptions. You need to solve the complete set of Maxwell equations, not just one!
 
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  • #33
vanhees71 said:
You need to solve the complete set of Maxwell equations, not just one!
I agree completely with this and all of my comments are assuming that we are looking for solutions to all of Maxwell's equations.
 
  • #34
You don't need relativity or tensors to get a grip on this problem. You do need to use dynamic rather than static potentials; for example, the familiar E -= -∇V changes to E = -∇V - μ ∂A/∂t
where A is the vector potential such that H = ∇ x A = B
and V is the scalar electric potential;
and Poisson's equation changes to ∇2V = -ρ/ε - μ ∂/∂t (∇⋅A) etc.
If you try to use static potentials you get that the E field around even a time-varying current is zero.
EDIT: I was assuming a long wire but what I said can be applied to your coil also.
The idea of retardation potentials is included in what I said FYI.
 
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