Integrating Charge Conservation Equation with Dirac Delta Function

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Homework Help Overview

The discussion revolves around integrating a charge conservation equation involving the Dirac delta function in the context of classical electrodynamics. The original poster is attempting to understand the integration of a specific equation that includes a time derivative and the delta function.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants are exploring the nature of the derivative in the equation, questioning whether it is an ordinary or partial derivative. There is also a discussion about the interpretation of the delta function as either a constant or an impulse function. The original poster expresses uncertainty about their solution and seeks clarification on the integration process.

Discussion Status

Some participants have provided clarifications regarding the type of derivative involved and the nature of the Dirac delta function. The original poster has acknowledged this clarification and is focusing on the left-hand side of the equation, indicating a step-by-step approach to solving the problem.

Contextual Notes

The original poster mentions the need to show the equality of both sides of the equation related to charge conservation, referencing a specific source for the equation. There is an indication of needing further assistance with the integration process before tackling the right-hand side of the equation.

jmwilli25
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Homework Statement



I just need help integrating this equation.
e is just the charge of an electron so it is constant



Homework Equations




[tex] -\int_{V}d\vec{r}\frac{\delta}{\delta t}e\delta(\vec{r}-\vec{R}(t))[/tex]

The Attempt at a Solution



[tex] -e\frac{d}{dt}\int_{V}d\vec{r}\delta(\vec{r}-\vec{R}(t))[/tex]
[tex] -e\frac{d}{dt}4\pi[/tex]

I don't believe my solution is correct or complete
 
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Some additional context would be helpful/necessary. Is the derivative an ordinary derivative like this?
[tex]-\int_{V}d\vec{r}\frac{d}{dt}e\delta(\vec{r}-\vec{R}(t))[/tex]

or is a partial derivative, like this?
[tex]-\int_{V}d\vec{r}\frac{\partial}{\partial t}e\delta(\vec{r}-\vec{R}(t))[/tex]

Is [itex]\delta[/itex] just a constant, or are you indicating an impulse function?
 
I think he maybe referring to functional differentiation, not too sure though.
 
Sorry, it is the partial derivative inside the integral and
[tex] \delta(\vec{r}-\vec{R}(t))[/tex]
is the dirac delta function.

Context: I am trying to show that the equation of charge conservation holds when
[tex] \rho(\vec{r},t)=e\delta(\vec{r}-\vec{R}(t))[/tex]

The entire equation that I am trying to solve is
[tex] -\int_{V}d\vec{r}e\frac{\partial}{\partial t}e\delta(\vec{r}-\vec{R}(t))=\int_{V}d\vec{r}\vec{\nabla}\bullet(e\frac{d}{dt}\delta(\vec{r}-\vec{R}(t))).[/tex]
I have to show that the two sides are equal.
But I figured if I could get help just with the LHS then I might be able to do the RHS myself. Granted, I still need to figure out how to apply the divergence to a full derivative of time, but one step at a time. Also, the equation that I have just given is exactly what is in the book. Classical Electordynamics, Schwinger 1998.
 

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