Vector Integration: Fundamental theorem use

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SUMMARY

The discussion centers on the application of the divergence theorem in vector calculus, specifically illustrating the equation $$\int_{V} \nabla \cdot (f\vec{A}) \ dv = \int_{V} f( \nabla \cdot \vec{A} ) \ dv + \int_{V} \vec{A} \cdot (\nabla f ) \ dv = \oint f\vec{A} \cdot \ d\vec{a}$$. The divergence theorem is confirmed to facilitate the transition from the volume integral of the divergence of the vector field $$\vec{B} = f\vec{A}$$ to the surface integral $$\oint f\vec{A} \cdot d\vec{a}$$. This relationship is crucial for understanding how scalar and vector fields interact in integral forms.

PREREQUISITES
  • Understanding of vector calculus concepts, particularly divergence and gradient.
  • Familiarity with the divergence theorem and its applications.
  • Knowledge of scalar and vector fields in mathematical physics.
  • Ability to manipulate integrals involving vector fields.
NEXT STEPS
  • Study the proof and applications of the divergence theorem in various contexts.
  • Explore the relationship between scalar fields and vector fields in integral calculus.
  • Learn about the implications of vector calculus in physics, particularly in fluid dynamics.
  • Investigate advanced topics such as Stokes' theorem and its connection to the divergence theorem.
USEFUL FOR

Students of mathematics and physics, particularly those studying vector calculus, as well as educators looking to clarify the application of the divergence theorem in real-world scenarios.

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Homework Statement



Could someone illustrate why
$$\int_{V} \nabla \cdot (f\vec{A}) \ dv = \int_{V} f( \nabla \cdot \vec{A} ) \ dv + \int_{V} \vec{A} \cdot (\nabla f ) \ dv = \oint f\vec{A} \cdot \ d\vec{a}$$
?

Homework Equations

The Attempt at a Solution


I understand that the integrand can be split by using vector product rules to give two integrals, but I don't see how the divergence theorem,
$$\int_{V} (\nabla \cdot \vec{A}) \ dv = \oint \vec{A} \cdot d\vec{a}$$
gets me from step 2 to 3.

Assistance is greatly appreciated!
 
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The divergence theorem takes you directly from step 1 to step 3. Define
$$\vec B= f\vec{A}$$ Then
$$\int_{V} (\vec{\nabla} \cdot \vec{B}) \ dv = \oint \vec{B} \cdot d\vec{a}=\oint f\vec{A} \cdot d\vec{a}$$
 
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kuruman said:
The divergence theorem takes you directly from step 1 to step 3. Define
$$\vec B= f\vec{A}$$ Then
$$\int_{V} (\vec{\nabla} \cdot \vec{B}) \ dv = \oint \vec{B} \cdot d\vec{a}=\oint f\vec{A} \cdot d\vec{a}$$

I see it now, thank you very much!
 

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