Question about topology in study of electricity

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Discussion Overview

The discussion revolves around the relationship between topology and electric flux in the context of physics and mathematics. Participants explore how different geometric shapes, such as spheres, cubes, and tori, affect the calculation of electric flux and the implications of these shapes' topological properties.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the flux is the same for a sphere and a cube surrounding an electric field due to their topological similarities.
  • Another participant explains that the flux through a sphere and a cube can be shown to be equal under certain conditions, referencing Gauss's law and the absence of charge in the region between the two shapes.
  • A participant raises a question about how to determine the orientations of the surfaces involved in the flux calculations, suggesting that orientations may be assigned arbitrarily.
  • Another participant clarifies that for proper calculations, the sphere and cube should have the same orientation, and discusses the implications of opposite orientations on the flux values.
  • One participant draws a connection between the discussion and concepts from homology, suggesting a deeper mathematical relationship between particles and flux.

Areas of Agreement / Disagreement

Participants express differing views on the implications of topology for electric flux calculations, and there is no consensus on the effects of different shapes or orientations on the flux values.

Contextual Notes

The discussion includes assumptions about the absence of charge in certain regions and the definitions of orientations, which may affect the interpretations of the flux calculations.

Coolphreak
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This question pertains to physics, but has to do with the math. In order to find the flux of an electric field you can put a sphere around it and use that to find flux, since the amount leaving is the same at every point. My teacher said that if you put a cube around the field/charge, you would get the same amount of flux, but it would be a much more difficult computation. My question is, is the flux the same because the sphere and the cube have the same topology? what happens if you put the field inside a torus? Would the amount of flux calculated be different?
 
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For simplicity, suppose that the sphere is inside the cube. We can define the region R which lies between the sphere and the cube. R has two boundaries: the cube (oriented positively) and the sphere (oriented negatively) We have:

flux through sphere + flux through R
= flux through sphere + (flux through cube - flux through sphere)
= flux through cube


Intuitively, if there is no charge in R, then there is no source of electromagnetic flux. Therefore, the net flux through R must be zero, and so the flux through the sphere is equal to the flux through the cube.

Rigorously, it depends on your definitions, but it essentially boils down to applying some form of Gauss's law to R; the net flux through the boundary is proportional to the net charge inside R.
 
How do you determine the orientations? Are they assigned arbitrarily? Your explanation reminds me a bit of homology lol
 
Last edited:
Coolphreak said:
How do you determine the orientations?
Well, to do the problem properly, I simply need the sphere and cube to have the same orientation. I chose the orientation on my region so that it would agree with the cube's orientation and disagree with the sphere's orientation.

Note that if the sphere and the cube had opposite orientations, the flux through the sphere would be the negation of the flux through the cube!


Your explanation reminds me a bit of homology lol
As well it should! For example, if you're using point particles, then I believe that it can be fruitful to think of your particles as punctures in 3-space and flux as a linear functional on 2-chains.
 

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