D'Alambert Equation: Solving for $\psi(\vec{r},t)$

  • Context: Graduate 
  • Thread starter Thread starter Petar Mali
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around solving the D'Alembert equation for the function $\psi(\vec{r},t)$, particularly in the context of different forms of the source term $g(\vec{r},t)$. Participants explore various methods and conditions under which solutions may exist.

Discussion Character

  • Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant presents a proposed solution for $\psi(\vec{r},t)$ in terms of a function $F_1(t-\frac{r}{\upsilon})$.
  • Another suggests using spherical coordinates and separation of variables as a method to approach the problem.
  • Some participants challenge the validity of the proposed solution, arguing that it cannot hold for a nontrivial source term $g(\vec{r},t)$ on the right-hand side of the equation.
  • Others acknowledge that while the proposed solution may not work for a general $g(\vec{r},t)$, specific cases, such as $g(r,t)=0$, could yield valid solutions.
  • A participant questions the assumption that the initial formula could be a solution for cases where $g(\vec{r},t)$ is non-zero.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as there are competing views regarding the applicability of the proposed solution depending on the nature of the source term $g(\vec{r},t)$.

Contextual Notes

Limitations include the dependence on the specific form of $g(\vec{r},t)$ and the assumptions made regarding the solution's validity in different scenarios.

Petar Mali
Messages
283
Reaction score
0
[tex]\Delta\psi(\vec{r},t)-\frac{1}{\upsilon^2}\frac{\partial^2\psi(\vec{r},t)}{\partial t^2}=-g(\vec{r},t)[/tex]

How to get solution

[tex]\psi(\vec{r},t)=\frac{1}{r}F_1(t-\frac{r}{\upsilon})[/tex]

where [tex]F_1[/tex] is any function of argument [tex]t-\frac{r}{\upsilon}[/tex].
 
Physics news on Phys.org
Write the laplacian in spherical coordinates, and use separation of variables.
 
Your [tex]\psi[/tex] can not be a solution for a nontrivial [tex]g(r,t)[/tex] on the rhs.
 
Well, not for a general g(r,t) but there are solutions for some specific, non-trivial functions.
 
HallsofIvy said:
Well, not for a general g(r,t) but there are solutions for some specific, non-trivial functions.

For instance for g(r,t)=0. Where did you get the idea that your formula is a solution for a non-zero g?
 

Similar threads

  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 7 ·
Replies
7
Views
4K
  • · Replies 36 ·
2
Replies
36
Views
6K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 0 ·
Replies
0
Views
3K
  • · Replies 5 ·
Replies
5
Views
4K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K