Divergence theorem for a non-closed surface?

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Discussion Overview

The discussion revolves around the application of the divergence theorem (Gauss' theorem) to non-closed surfaces, specifically exploring whether it can be used for an open surface with boundaries, such as a paraboloid that does not have a top plane. Participants seek to clarify the conditions under which the theorem might be applicable or if alternative approaches exist.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions the applicability of the divergence theorem to an open surface, seeking clarification on conditions for its use.
  • Another participant suggests that the theorem can be applied to the paraboloid if a plane is added, allowing for the calculation of flux through the closed surface and then subtracting the flux through the plane to find the flux through the paraboloid.
  • A third participant argues that discussing the divergence theorem for non-closed surfaces is nonsensical due to the theorem's derivation, which relies on the concept of closed surfaces and the flux contributions from outward-facing sides of infinitesimal cubes.
  • One participant mentions the existence of Stokes' theorem as an alternative for open surfaces.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of the divergence theorem to non-closed surfaces, with no consensus reached on whether it can be used directly or indirectly. The discussion remains unresolved regarding the validity of applying the theorem in this context.

Contextual Notes

Limitations include the lack of clarity on specific conditions under which the divergence theorem might be applied to non-closed surfaces and the assumptions underlying the derivation of the theorem itself.

NicolasM
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Is there some way we can apply divergence (Gauss') theorem for an open surface, with boundaries? Like a paraboloid that ends at some point, but isn't closed with a plane on the top.

I found this at Wikipedia:
It can not directly be used to calculate the flux through surfaces with boundaries

but I couldn't find some further explanation, like under what conditions it can be applied, or in what way we can "indirectly" use it.
 
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Well you can use divergence theorem to calculate flux through your paraboloid WITH plane attached. Then if you can calculate flux through the plane you can substract it from what you got; what is left is obviously flux through paraboloid.
 
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IMHO, it makes no sense to speak of the divergence theorem for a non-closed surface because of the way the theorem is derived. I don't know if you already know this (or maybe I'm the one who lacks knowledge) but in the derivation of this theorem one makes reference to the addition of the flux in all infinitesimally small cubes that make up a surface and the only flux that "survives" is the one from the outward facing-sides on the most exterior cubes of your closed surface.
 
No, but there is a curl theorem for open surfaces (stokes)
 

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