How to Show the General Solution to the Poisson Equation?

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SUMMARY

The discussion centers on demonstrating the general solution to the Poisson equation, specifically \(\nabla^2 \Phi = -\frac{\rho(r)}{\epsilon}\). The solution is expressed as \(\Phi(r) = \frac{1}{4\pi\epsilon} \int d^3r' \left(\frac{\rho(r')}{|r - r'|}\right)\). The participants explore the implications of the given boundary condition \(\nabla^2 \frac{1}{r} = -4\pi\delta^3(r)\) and its relevance to solving the Poisson equation. Clarifications on the relationship between electric and gravitational potentials in this context are also discussed.

PREREQUISITES
  • Understanding of the Poisson equation and its applications in physics.
  • Familiarity with vector calculus, particularly the Laplacian operator.
  • Knowledge of delta functions and their role in boundary conditions.
  • Basic concepts of electric and gravitational potential.
NEXT STEPS
  • Study the derivation of the Poisson equation from electrostatics and gravitational theory.
  • Learn about the properties and applications of delta functions in physics.
  • Explore the method of Green's functions for solving partial differential equations.
  • Investigate the relationship between electric potential and gravitational potential in classical mechanics.
USEFUL FOR

Students and professionals in physics, particularly those focused on electromagnetism and gravitational theory, as well as anyone interested in solving partial differential equations in applied mathematics.

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Homework Statement



Given that [tex]\nabla[/tex]2 1/r = -4[tex]\pi[/tex][tex]\delta[/tex]3(r)

show that the solution to the Poisson equation [tex]\nabla[/tex]2[tex]\Phi[/tex] = -([tex]\rho[/tex](r)/[tex]\epsilon[/tex])

can be written:

[tex]\Phi[/tex](r) = (1/4[tex]\pi[/tex][tex]\epsilon[/tex]) [tex]\int[/tex] d3r' ([tex]\rho[/tex](r') / |r - r'|)


Homework Equations





The Attempt at a Solution



I know that the Poisson equation is kind of like a partial differential equation. I rearranged it to [tex]\Phi[/tex]rr(r2) + [tex]\Phi[/tex]r(2r) = [-[tex]\rho[/tex](r) * r2 ] / [tex]\epsilon[/tex]

But that wasn't very helpful

Then I also realized that the equations for electric potential is a solution to this... but that is only a special case. Also, is gravitational potential also a solution, or no?

How do you solve this type of equation? What does the 'given': [tex]\nabla[/tex]2 1/r = -4[tex]\pi[/tex][tex]\delta[/tex]3(r)
even tell me? I am very lost. I read up about Poisson equations and I think the 'given' is like a boundary case... but I don't know how you incorporate the boundary case of a Poisson equation into a solution.
 
Last edited:
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Just take the Laplacian of the proposed solution (Remember, you don't actually have to solve Poisson's equation to show that something is a solution of it)...what do you get?
 

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