Surface Integral Homework: Compute F = <z,x,y> f(x,y)

In summary, The divergence theorem requires the surface integral to be over the whole surface of the enclosed solid. Therefore, in order to correctly apply the theorem and get a result of 0, you must also calculate the surface integral over the sides and bottom of the enclosed solid. However, if the problem only asks for the flux through the top face, then your solution of -1 is correct.
  • #1
brtgreen
11
0

Homework Statement


Compute surface integral. F = <z, x, y> f(x,y) = x + y, 0 <= x <= 1, 0 <= y <= 1.

Homework Equations


The Attempt at a Solution



Well this is what I tried:

<z, x, y > * < -fx, -fy, 1> = -z - x + y = -(x+y) - x + y = -2x
Then I integrated it using the bounds given and got -1.

But by the divergence theorem this should = 0. Help!
 
Physics news on Phys.org
  • #2
The divergence theorem requires the surface integral to be over the whole surface of the enclosed solid. You only did the top surface, which you did correctly. But what about the sides and bottom?
 
  • #3
Oh ok I get what you're saying. But how am I supposed to know if they're asking for just the top or the whole enclosed surface?
 
  • #4
brtgreen said:
Oh ok I get what you're saying. But how am I supposed to know if they're asking for just the top or the whole enclosed surface?

I guess you would have to just read the question carefully. And remember, the divergence theorem only applies in a situation where you have a surface enclosing a volume and it always requires the surface integral to be over the whole surface.

On the other hand, if your problem asked you to calculate the flux through the top face, you are done already.
 

1. What is a surface integral?

A surface integral is a mathematical concept used in vector calculus to calculate the flux of a vector field across a surface. It involves integrating a function over a surface, similar to how a regular integral involves integrating a function over an interval.

2. How do you compute a surface integral?

To compute a surface integral, you first need to determine the limits of integration for the surface. Then, you need to set up the integral using the formula for surface integrals, which involves the vector field and the surface element. Finally, you can solve the integral using appropriate techniques, such as changing variables or using symmetry.

3. What is the difference between a surface integral and a regular integral?

A surface integral involves integrating a function over a surface, whereas a regular integral involves integrating a function over an interval. In other words, a surface integral is two-dimensional while a regular integral is one-dimensional.

4. What is the significance of computing a surface integral?

Computing a surface integral allows us to calculate the amount of flux, or flow, of a vector field across a surface. This has many practical applications, such as in fluid mechanics, electromagnetism, and physics.

5. Can you provide an example of computing a surface integral?

Sure, let's say we have a vector field F = and we want to compute the surface integral of F over the surface given by z = 2x + 3y, for the region bounded by the x-y plane, the y-z plane, and the x-z plane. We would set up the integral as ∫∫R F · dS, where R is the region bounded by the planes. We can then solve the integral using appropriate techniques, such as changing variables, to get the final result.

Similar threads

  • Calculus and Beyond Homework Help
Replies
7
Views
683
  • Calculus and Beyond Homework Help
Replies
2
Views
507
  • Calculus and Beyond Homework Help
Replies
6
Views
548
  • Calculus and Beyond Homework Help
Replies
13
Views
1K
  • Calculus and Beyond Homework Help
Replies
8
Views
468
  • Calculus and Beyond Homework Help
Replies
6
Views
757
  • Calculus and Beyond Homework Help
Replies
3
Views
606
  • Calculus and Beyond Homework Help
Replies
3
Views
1K
  • Calculus and Beyond Homework Help
Replies
2
Views
1K
  • Calculus and Beyond Homework Help
Replies
8
Views
875
Back
Top