Therefore \oint_{S}\vec{r}\cdot\vec{n}dS=3V

Click For Summary

Discussion Overview

The discussion revolves around evaluating the surface integral \(\oint_{S} \vec{r} \cdot \vec{n} dS\) where \(S\) is a closed surface. Participants explore the application of the divergence theorem in this context, discussing the implications and calculations involved.

Discussion Character

  • Exploratory, Technical explanation, Mathematical reasoning

Main Points Raised

  • One participant requests assistance with evaluating the integral, indicating a need for clarification on the problem.
  • Another participant seeks to clarify the notation used in the integral, distinguishing between two forms of the expression.
  • A later reply suggests using the divergence theorem, stating that \(\vec{r} = x\vec{i} + y\vec{j} + z\vec{k}\) leads to the conclusion that the integral evaluates to \(3V\), where \(V\) is the volume.
  • Another participant acknowledges the frequent appearance of the divergence theorem in their studies, indicating a recognition of its relevance.
  • Further elaboration on the application of the divergence theorem is provided, reiterating that \(\int_{S} \vec{r} \cdot \vec{n} dS\) equals \(\int_{V} \nabla \cdot \vec{r} dV\) and confirming the result as \(3V\).

Areas of Agreement / Disagreement

Participants appear to agree on the application of the divergence theorem and the resulting evaluation of the integral as \(3V\). However, there is no explicit consensus on the initial interpretation of the integral or its notation.

Contextual Notes

Some participants express uncertainty regarding the notation and the initial setup of the problem, which may affect their understanding of the integral's evaluation.

galipop
Messages
51
Reaction score
0
Hi All,

I've been working through a series of vector calculus problems and I need some help to get started with this one. Anyone care to help?

The problem is:

Evaluate [tex]\oint_{s} r.n.dS[/tex] where S is a closed surface.

Cheers
 
Physics news on Phys.org
What is the meaning of this?
a)[tex]\int_{S}r\vec{n}\cdot{d}\vec{S}[/tex]
b)[tex]\int_{S}\vec{r}\cdot\vec{n}dS[/tex]
 
b)

sorry I didn't know how to do the vector symbol.
 
Use the divergence theorem:
[tex]\vec{r}=x\vec{i}+y\vec{j}+z\vec{k}[/tex]
Hence, the answer is 3V, where V is the volume.
 
Ok I'll give it a try. Hmm I keep noticing the divergence theorem popping up.
 
OK then:

[tex]\int_{S}\vec{r}\cdot\vec{n}dS = \int_{V}\nabla\cdot\vec{r}dV[/tex]

Therefore
[tex]\int_{V}\nabla\cdot\vec{r}dV=\int_{V}3dV[/tex]
[tex]=3V[/tex]
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 13 ·
Replies
13
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 5 ·
Replies
5
Views
15K
  • · Replies 13 ·
Replies
13
Views
1K
  • · Replies 6 ·
Replies
6
Views
3K
Replies
4
Views
3K