# Surface Integral of a Vector Field

• December 4th 2012, 11:45 PM
aforl
Surface Integral of a Vector Field
Hi guys, need some assurance here in evaluating this surface integral.

$\iint_{S} \mathbf{F}\cdot d\mathbf{S}$
where

$\mathbf{F} = \left \langle x^2+y^2+z^2, -2xy+\sin(z), 2z \right \rangle, (x,y,z)\in \mathbb{R}^3$
and

$S:x^2+y^2+(z-5)^2=1$ with positive orientation (outward pointing normal).

Here's what I did:
Using Green's theorem (Divergence theorem)

$\textup{div }\mathbf{F}=2x-2x+2=2$

$\iint_{S} \mathbf{F}\cdot d\mathbf{S}= \iiint_{E} \textup{div }\mathbf{F } dV$
$=2\iiint_{E} dV=2(\textup{volume of sphere})=2( \frac{4}{3} \pi r^3 )=\frac{8\pi}{3}$

Anything wrong with what I did?
• December 6th 2012, 03:35 AM
aforl
Re: Surface Integral of a Vector Field
Bump... Not even a 'OK' or 'Good' or 'Wrong'?

Lol I've done the question already, only need someone to assure me this is the right way to go.
• December 6th 2012, 09:40 AM
HallsofIvy
Re: Surface Integral of a Vector Field
I thought I had responded to this, yesterday. Did you post on more than one forum?

Yes, what you have done is completely correct. I considered suggesting you check by doing the surface integral directly but that "sin(z)" makes things horrible!
• December 7th 2012, 06:39 AM
aforl
Re: Surface Integral of a Vector Field
Quote:

Originally Posted by HallsofIvy
I thought I had responded to this, yesterday. Did you post on more than one forum?

Yes, what you have done is completely correct. I considered suggesting you check by doing the surface integral directly but that "sin(z)" makes things horrible!

Thanks! :)
Yes I posted on another forum, on which you replied as well. Thanks for both instances! :)