Solutions to laplace's equation & uniqueness thrm #2 (Griffiths)

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Discussion Overview

The discussion revolves around the uniqueness theorems related to Laplace's equation and Poisson's equation as presented in Griffiths' "Introduction to Electrodynamics." Participants explore the implications of the second uniqueness theorem, particularly in relation to charge density and the conditions under which the electric field is determined.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions whether the specified charge density ρ refers to the region of space for which the potential is being determined or to the conductors/insulators.
  • Another participant clarifies that the charge density ρ pertains to the volume V where the electric field is being solved.
  • A participant expresses confusion regarding the applicability of the uniqueness theorems, suggesting that uniqueness theorem 1 applies to both Laplace's and Poisson's equations, while uniqueness theorem 2 is specific to Poisson's equation.
  • Another participant confirms that uniqueness theorem 2 is indeed for Poisson's equation and uniqueness theorem 1 is for Laplace's equation.

Areas of Agreement / Disagreement

Participants generally agree on the distinction between the uniqueness theorems, but there is some uncertainty regarding the specific applications of each theorem and the interpretation of charge density.

Contextual Notes

The discussion does not resolve the nuances of how charge density is treated in relation to the uniqueness theorems, nor does it clarify the implications of these theorems in different contexts.

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In griffith's intro to electrodynamics (4rth edition), ch. 3, pg. 121.

here is the second uniqueness thrm for the solutions to laplace's equation:

Second uniqueness thrm: In a volume V surrounded by conductors and containing a specified charge density ρ, the electric field is uniquely determined if the total charge on each conductor is given.

the only part I'm confused about is, in the beginning where he says "in a volume V surrounded by conductors and containing a specified charge density ρ"

Q: is the charge density ρ referring to that belonging to the region of space whose potential we're trying to determine? or is it referring to that of the conductor/insulator?

thanks
 
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It is referring to that belonging to the volume V in which we are solving for the electric field.
 
thought so!

but then this leads to another confusion. I thought both uniqueness theorems were meant for the solutions to the laplace equation. The laplace equation however does not deal with charges inside the region.

so then, i guess, uniqueness thrm 1 is for both the laplace & the poisson equations while uniqueness thrm 2 is for just the poisson eqn?

please confirm this for me
 
Uniqueness theorem 2 is for Poisson's and uniqueness theorem 1 is for Laplace's.
 

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