Is This the Correct Method to Compute Flux Integral Over Cylinder Walls?

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    Cylinder Flux Integral
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SUMMARY

The discussion centers on computing the flux integral over the walls of a cylinder oriented along the z-axis using the vector field \(\vec{F}\) and the gradient of the function \(G(x,y,z) = r^{2} = x^{2} + y^{2}\). The gradient is calculated as \(\nabla G = <2x, 2y, 0>\). While one participant suggests using the Divergence Theorem for a more straightforward solution, the original poster seeks to compute the flux integral directly without employing the theorem. The discussion confirms that the proposed method is valid for calculating the flux integral over the cylinder's walls.

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IniquiTrance
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To compute the flux integral over a cylinder's walls oriented along the z axis:

Can I do:

[tex]\int\int \vec{F}\cdot\nabla G(x,y,z) dA[/tex]

[tex]G(x,y,z) = r^{2}=x^{2}+y^{2}[/tex]

[tex]\nabla G = <2x, 2y, 0>[/tex]

[tex]\int\int \vec{F}\cdot <2x,2y,0> dA[/tex]

Is this a correct approach?
 
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IniquiTrance said:
To compute the flux integral over a cylinder's walls oriented along the z axis:

Can I do:

[tex]\int\int \vec{F}\cdot\nabla G(x,y,z) dA[/tex]

[tex]G(x,y,z) = r^{2}=x^{2}+y^{2}[/tex]

[tex]\nabla G = <2x, 2y, 0>[/tex]

[tex]\int\int \vec{F}\cdot <2x,2y,0> dA[/tex]

Is this a correct approach?

Assuming a positive orientation, the easiest way to do it is by Divergence Theorem.

(1) Find the divergence of [tex]\vec{F}[/tex]

(2) Integrate this over the solid cylinder.

The other way is to split the cylinder into 3 pieces the Top, Bottom and Side and the sum the flux contributed from each piece.
 
~Death~ said:
Assuming a positive orientation, the easiest way to do it is by Divergence Theorem.

(1) Find the divergence of [tex]\vec{F}[/tex]

(2) Integrate this over the solid cylinder.

The other way is to split the cylinder into 3 pieces the Top, Bottom and Side and the sum the flux contributed from each piece.

Thanks for the reply.

Yeah, I specifically want to solve it as a flux integral without the div theorem.

Also know how to split it up. Is this a proper way to compute it over the cylinder walls though?
 

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