Definition for Surface Integral

In summary, Line Integral and Surface Integral are two different types of integrals, with the latter being a double integral while the former is a single integral. They can be connected through the Stoke's Theorem. The traditional definition of Surface Integral is \int\int_S\vec{f}\cdot \hat{n}\;dS, while defining it as \int\int_S\vec{f}\cdot d\vec{r} is not equivalent. The statement "dx = dy \wedge dz" is nonsensical.
  • #1
Jhenrique
685
4
Hello!

The definition of Line Integral can be this:
[tex]\int_s\vec{f}\cdot d\vec{r}=\int_s(f_1dx+f_2dy+f_3dz)[/tex]

And the definition of Surface Integral can be this:
[tex]\int\int_S(f_1dydz+f_2dzdx+f_3dxdy)[/tex]

However, in actually:
[tex]\\dx=dy\wedge dz \\dy=dz\wedge dx \\dz=dx\wedge dy[/tex]
What do the Surface Integral be equal to:
[tex]\int\int_S(f_1dy\wedge dz+f_2dz\wedge dx+f_3dx\wedge dy)=\int\int_S(f_1dx+f_2dy+f_3dz)=\int\int_S\vec{f}\cdot d\vec{r}[/tex]

I know, I know... I know that, generally, the definition to Integral Surface is:
[tex]\int\int_S\vec{f}\cdot \hat{n}\;dS[/tex]
I until like this definition when compared to its respective Line Integral:
[tex]\int_s\vec{f}\cdot \hat{t}\;ds[/tex]

But, is correct to definite the Surface Integral as:
[tex]\int\int_S\vec{f}\cdot d\vec{r}[/tex]
being
[tex]d\vec{r}=(dx,dy,dz)[/tex]
?
 
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  • #2
No, the surface integral is, as you say, a double integral while the path integral is a single integral. They are NOT the same thing. They can, of course, be connected by, for example, the Stoke's Theorem that says that the integral of the curl of [itex]\vec{F}[/itex] over a surface is the same as the integral of [itex]\vec{F}[/itex] around the boundary of the surface.
 
  • #3
But I definited the Surface Integral with a double integral (as you can see below or above)
[tex]\int\int_S\vec{f}\cdot d\vec{r}[/tex]
with the only difference that I used the position vector r, like in Line Integral. But, second the identities above, to define the Surface integral with ·dr is equivalent to traditional definition, with ·ndS. Correct!?
 
  • #4
Jhenrique said:
the Surface integral with ·dr is equivalent to traditional definition, with ·ndS. Correct!?

what? your definitions make no sense. [itex]``dx = dy \wedge dz''[/itex] is literally nonsensical.
 

What is a surface integral?

A surface integral is a mathematical concept used in multivariable calculus to calculate the flux of a vector field through a surface. It involves breaking the surface into small pieces and summing up the contributions from each piece to find the total flux.

What are the applications of surface integrals?

Surface integrals have various applications in physics and engineering, such as calculating electric and magnetic flux, fluid flow, and heat transfer. They are also used in computer graphics to determine the amount of light that is reflected or absorbed by a surface.

How is a surface integral different from a line integral?

A surface integral is a double integral over a two-dimensional surface, while a line integral is a single integral over a one-dimensional curve. They both involve integrating a function over a certain domain, but the dimension of the domain is what sets them apart.

What is the significance of the direction of the surface normal in a surface integral?

The direction of the surface normal determines the orientation of the surface, which is crucial in calculating the flux through the surface. If the surface has a positive orientation, the flux will be positive, and if it has a negative orientation, the flux will be negative.

Can surface integrals be evaluated using different coordinate systems?

Yes, surface integrals can be evaluated using different coordinate systems such as Cartesian, cylindrical, or spherical coordinates. The choice of coordinate system depends on the shape of the surface and the given vector field. Some coordinate systems may be more convenient for certain problems than others.

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