Flux integral and Gauss's theorem

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Homework Help Overview

The discussion revolves around calculating the flux of a given vector field, v(x,y,z) = (y, x, z-x), out of a unit cube defined by the coordinates x, y, z = [0,1]. Participants are also tasked with applying Gauss's theorem to verify the flux calculation.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Some participants suggest calculating the flux by integrating the dot product of the vector field and the unit normal vector over each face of the cube.
  • Questions arise regarding the setup of the integral, particularly concerning the normal vectors and the components of the vector field.
  • There is a request for clarification on how to approach the integration for specific faces of the cube.

Discussion Status

The discussion is ongoing, with participants expressing uncertainty about how to begin the calculations. Some guidance has been offered regarding the integration process for the cube's faces, but there is no explicit consensus on the approach yet.

Contextual Notes

Participants have reiterated the problem statement multiple times, indicating a need for clarity on the initial steps. There is also a focus on ensuring that the calculations align with Gauss's theorem.

adgar
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Homework Statement


Please help me to solve this assignment.
[/B]
a) A vector field is given by v(x,y,z) = (y, x, z-x).
Calculate the flux from this field out of the unit cube, given by x,y,z = [0,1].

b) Use Gauss's theorem to calculate the same flux. Check that you get the same result.

Homework Equations


Electric Flux: Φ = E. A .cosθ
Electric Flux: Φ = ∫ E. dA = Qencl / ε

The Attempt at a Solution


For part a) one can calculate ∫∫ v . n dxdy, where n is the unit normalvector for the surface A, for each cube faces and add them together.
 
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Well ?
 
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I just don't know how to start!
 
adgar said:
I just don't know how to start!
 
adgar said:

Homework Statement


Please help me to solve this assignment.
[/B]
a) A vector field is given by v(x,y,z) = (y, x, z-x).
Calculate the flux from this field out of the unit cube, given by x,y,z = [0,1].

b) Use Gauss's theorem to calculate the same flux. Check that you get the same result.

Homework Equations


Electric Flux: Φ = E. A .cosθ
Electric Flux: Φ = ∫ E. dA = Qencl / ε

The Attempt at a Solution


For part a) one can calculate ∫∫ v . n dxdy, where n is the unit normalvector for the surface A, for each cube faces and add them together.
 
Take one of the faces of the unit cube and write out ##\vec v \cdot \hat n## then integrate over that face. Proceed to the next face, etc. Repeat until done !
 
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adgar said:

Homework Statement


Please help me to solve this assignment.
[/B]
a) A vector field is given by v(x,y,z) = (y, x, z-x).
Calculate the flux from this field out of the unit cube, given by x,y,z = [0,1].

b) Use Gauss's theorem to calculate the same flux. Check that you get the same result.

Homework Equations


Electric Flux: Φ = E. A .cosθ
Electric Flux: Φ = ∫ E. dA = Qencl / ε

The Attempt at a Solution


For part a) one can calculate ∫∫ v . n dxdy, where n is the unit normalvector for the surface A, for each cube faces and add them together.
 
The flux through the face parallell to the z-axis, which I call for A1 and A2, is
Φ = ∫∫v.k dA1, where k is the normal vector in z-direction. But, what is V and dA1 now?!
Is v the z-component of the vector field?

I'm hoping someone can help walk me through this problem!
 
Do one face at the time. Both the face with x=1 and the face with y=1 are parallel to th z axis...
Or do you mean the face with z = 1 ? That is perpendicular to the z axis.
The normal in the z direction is the surface vector for the face with z = 1. In other words, (0,0,1)
A point on the surface is characterized by (x,y,z) = (x,y,1)

Can you now write out the integral for that face ?
 

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