Boundary conditions for Laplace's equation

  1. I don't seem to grasp the meaning of boundary conditions for Laplace's equation.

    Consider the Lagendre expansion of the potential at x due to a unit charge 1/|x-x'|, where x' is the position of the unit point charge.
    To do the expansion, we need to consider a volume in space where the potential satisfies the Laplace equation. I can see that the potential satisfies Laplaces equation anywhere in space except at x=x', but what are the boundary conditions? Don't we have to know the potential at x=x', which is a boundary?
     
  2. jcsd
  3. Am I too vague in my question?
     
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