Solving Vector Field Flux with Gauss & Stokes

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Discussion Overview

The discussion revolves around demonstrating that the flux of the vector field \(\nabla \times A\) through a closed surface is zero, utilizing both Gauss's theorem and Stokes' theorem. Participants explore theoretical approaches and mathematical identities relevant to the problem.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant suggests starting with definitions of flux over a closed surface and the implications of Gauss's and Stokes' theorems on integrals.
  • Another participant provides the expression for the curl of vector field \(A\) and inquires about substituting this into Gauss's theorem.
  • A later reply confirms that Stokes' theorem may not be necessary for this problem, implying a preference for using Gauss's theorem alone.
  • Another participant proposes a method of splitting a closed surface into two surfaces and applying Stokes' theorem to analyze the flux, suggesting a spherical surface with the equator as a defining curve for clarity.
  • This participant also notes that while substituting derivatives into Gauss's theorem could work, a more intuitive explanation may be preferable.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of Stokes' theorem, with some arguing it is not needed while others suggest it could provide a clearer understanding. The discussion remains unresolved regarding the best approach to demonstrate the flux being zero.

Contextual Notes

Participants reference various mathematical identities and theorems without fully resolving the implications of these identities or the assumptions underlying their approaches.

Who May Find This Useful

Students and educators interested in vector calculus, particularly those studying the applications of Gauss's and Stokes' theorems in physics and engineering contexts.

galipop
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Hi folks,

I'm working on the following problem...

Show that the flux of the vector field [tex]\nabla \times A[/tex] through a closed surface is zero. Use both Gauss and Stokes.

Where can I begin?

Thanks...
 
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From the definitions. What is the flux over a closed surface, and what do the mentioned theorems allow you to do to integrals etc, and what identities do you know that might be useful. write them ot and use them.
 
Ok I started using this...

[tex]\nabla\times A = (\frac{\partial r}{\partial y}-\frac{\partial q}{\partial z})i + (\frac{\partial p}{\partial z}-\frac{\partial r}{\partial x})j+(\frac{\partial q}{\partial x}-\frac{\partial p}{\partial y})k[/tex]

Then...Gauss theorem

[tex]\int_V (\nabla \bullet A) dV[/tex]

So do I basically substitute the top eqn into Gauss's theorem?

Thanks
 
Yes - and I don't think you need Stokes' theorem in this.
 
the easiest way i can think of is taking a closed surface and splitting it into two surfaces with a single curve, then applying what you know about Stokes's theorem to the necessary values of the flux on the two surfaces. for example, consider a spherical surface, and then choose the equator as the defining curve. almost no equations needed, just plain logic. of course you could do the substitution of the derivatives and then show that the expression in the integral is zero using Gauss's theorem, but that's more writing (depending on if your teacher makes you prove the vector identity). i think that the first explanation is more "physically" satisfying.
 
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