Laplaces' s equation in spherical coordinates

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Discussion Overview

The discussion revolves around the formulation of Laplace's equation in spherical coordinates, specifically focusing on the constants used in the separation of variables, such as l(l+1) and the range of m from -l to l. Participants seek clarification on these aspects and their implications in different contexts, including electromagnetism and quantum mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the constants in the separation of Laplace's equation and requests detailed explanations or sources.
  • Another participant suggests that the form of the constants is derived from solutions with significant applications, hinting at connections to angular momentum quantum numbers.
  • A different participant mentions using series solutions for the polar part in electromagnetism and questions why the constraints on m are not evident from the series solution itself.
  • Another reply indicates that multi-pole expansion in electromagnetism will relate to the l and m values in Laplace's equation.
  • A repeated request for clarification on the constants and their significance is made, along with a link to a resource that may provide answers.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the reasons behind the specific forms of the constants or the implications of the constraints on m. Multiple viewpoints and questions remain unresolved.

Contextual Notes

Participants highlight the need for deeper understanding of the mathematical foundations and applications of Laplace's equation in spherical coordinates, indicating potential gaps in existing resources.

mjordan2nd
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After setting up Laplace's equation in spherical coordinates and separating the variables, it is not clear to me why the constants are put in the form of l(l+1) and why m runs from -l to l. Could anyone please help me ununderstand, or better yet, point me to a source that explains the entire process of separating Laplace's equation in spherical coordinates in detail? I have not been able to find anything on the internet whi h clarifies these points. It merely states them as facts.
 
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There is a quantum mechanics class in your immediate vicinity. You'd better have some light or you will get eaten by a Green function.

But seriously... They are put in that form because people found solutions that have important applications, and it was very convenient that way. You are going to find angular momentum quantum numbers popping out at you any second now, just as one example.
 
At this stage I'm trying to solve electromagnetism problems where recasting Laplace's equation into spherical coordinates seems useful. I am trying to use a series solution for the polar part. I have seen the quantum argumemt using operators to get the result, but I would think it should pop out of the series solution itself, especially the constraints on m. However, if that is the case I can't see it.
 
In E&M you will be seeing multi-pole expansion. And that is going to show up in the Laplace equation as well, also with the l and m values in the general scheme you have seen.

Keep going. It will become obvious why it is done that way.
 
mjordan2nd said:
After setting up Laplace's equation in spherical coordinates and separating the variables, it is not clear to me why the constants are put in the form of l(l+1) and why m runs from -l to l. Could anyone please help me ununderstand, or better yet, point me to a source that explains the entire process of separating Laplace's equation in spherical coordinates in detail? I have not been able to find anything on the internet whi h clarifies these points. It merely states them as facts.
You'll find the answer to why the constant is generally chosen as l(l+1) in http://www.luc.edu/faculty/dslavsk/courses/phys301/classnotes/laplacesequation.pdf
 

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