How can I solve for A in the Lorenz Gauge with a static source?

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Homework Help Overview

The discussion revolves around solving for the vector potential \(\vec{A}(x,t)\) in the context of the Lorenz Gauge, particularly with a static source represented by a delta function current density \(\vec{J}(x,t)=\vec{J}_0\delta(x-x_0)\). The original poster is grappling with the final steps of the problem after deriving the wave equation and its static form.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to simplify the wave equation and isolate terms to solve for \(\vec{A}\), expressing concern over the complexity introduced by the delta function and the limits of integration. Some participants suggest considering a plane wave solution or Fourier expansion as potential approaches. Others note that each component of \(\vec{A}\) can be treated as satisfying a scalar Poisson equation, hinting at the use of the Coulomb potential.

Discussion Status

The discussion is active, with various approaches being explored. Participants are providing hints and suggestions without reaching a consensus on a specific method. The original poster is seeking clarification on integrating the delta function and the implications of static sources.

Contextual Notes

There is an emphasis on the static nature of the sources, which implies no time dependence in the current or potential vectors. The original poster expresses uncertainty about the integration process and the treatment of the delta function in this context.

ApeXaviour
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I've gotten out most of this question, it's really just the last part that's getting to me at this stage. I'd never seen the http://mathworld.wolfram.com/DeltaFunction.html" before so it might be because of that. I've an idea how to do it but I just end up in a mess of partial derivatives. I'd say it's something simple I just can't see.

Homework Statement


"Demonstrate that in the Lorenz Gauge, [tex]\vec{A}(x,t)[/tex] satisfies a wave equation with the current density [tex]\vec{J}(x,t)[/tex] as source, and that for static sources this reduces to a Poisson-like equation.
Calulate [tex]\vec{A}(x,t)[/tex] for [tex]\vec{J}(x,t)=\vec{J}_0\delta(x-x_0)[/tex]"

Homework Equations


Lorentz guage: [tex]\vec{\nabla}\cdot\vec{A}=-\mu_0\epsilon_0\frac{dV}{dt}[/tex]
delta function:[tex]\int_{I}f(x)\delta(x-x_0)dx=f(x_0)[/tex]
(once [tex]I[/tex] includes the point [tex]x_0[/tex])
Otherwise [tex]\delta(x-x_0)=0[/tex]
and Maxwell's equations.

The Attempt at a Solution



The wave equation was relatively easy. Substituting the lorenz gauge into maxwell's equations and getting:
[tex]-\vec{\nabla}^2\vec{A}+\mu_0\epsilon_0\frac{\partial^2 \vec{A}}{\partial t^2}=\mu_0\vec{J}[/tex]For static sources
[tex]\vec{\nabla}\cdot\vec{A}=0[/tex]?
So the poisson like equation that you get comes up as: [tex]\vec{\nabla}\cdot V^2=-\frac{\rho}{\epsilon_0}[/tex]

Now for the last bit :frown: , since [tex]\vec{A}=\vec{A}(x,t)[/tex] then the wave equation can be simplified down to:
[tex]-\frac{\partial^2 \vec{A}}{\partial x^2}+\mu_0\epsilon_0\frac{\partial^2 \vec{A}}{\partial t^2}=\mu_0\vec{J_0}\delta(x-x_0)[/tex]
(with the [tex]J_0[/tex] term substituted in)

So how can I solve for A? My idea was to isolate [tex]d^2\vec{A}[/tex] and integrate to solve it but that gets too messy. Also over what limits would I integrate? +/- infinity? For the [tex]dx[/tex] that will give [tex]\vec{A}(x_0,t)[/tex]? What happens when I integrate the delta function in terms of [tex]dt[/tex]? I'd say there is something about the delta function that makes this fairly simple but I'm just not accustomed to it...

Thanks in advance for any hints you can give me...

Dec
 
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maybe, you can try [tex]A(x,t)[/tex] as a plane wave solution,
then you can get a solution
 
"Static sources' means no time dependence of the current vector, hence no time dependence of the potential vector.

To solve the eqn, Fourier expand all terms of the equation.
 
Each Cartesian component of A satisfies the scalar Poisson equation for a point charge, so just use the Coulomb potential for A_x, etc.
 

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