A question that uses divergence thm

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SUMMARY

The discussion focuses on applying the divergence theorem to derive the volume enclosed by a closed surface S, expressed as \(\frac{1}{3} \int_{S} \vec{x} \cdot d\vec{A}\). The user attempts to relate this to the volume integral \(V = \int_{V} dV\) and realizes that the divergence of the position vector \(\vec{x} = (x,y,z)\) is 3, confirming that \(\vec{x}\) is indeed a vector field. The simplification arises from recognizing that the divergence theorem allows for this transformation between surface and volume integrals.

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Homework Statement

show that the volume enclosed by a closed surface S is given by

## \frac{1}{3} \int_{S} \vec{x} \cdot d\vec{A} ##

Homework Equations

divergence theorem

The Attempt at a Solution



using divergence theorem

I get that ##V =\frac{1}{3} \int_{V} \nabla \cdot \vec{x} dV ##

but I want

## V = \int_{V} dV ## don't I? how does it simplify?
 
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Unless

## \vec{x} = (x,y,z) ##

Then:

## V = \frac{1}{3} \int_{V} (1+1+1) dV = \int_{V}dV ##

It's because x is just the position vector whose divergence is 3 isn't it? i.e. x is not a vector field?
 
Sure, that's it. But the position vector (x,y,z) IS a vector field. It's just a particular one.
 

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