Chapter 9: Vector Calculus
Section 9.9: Stokes' Theorem
Example 9.9.2
Show that the flux of the curl of F=z i−x j−y k through the unit sphere centered at the origin is necessarily zero.
Solution
Mathematical Solution
Evaluation of ∫∫S∇×F·N dσ requires the curl of F:
∇×F=ijk∂x∂y∂zz−x−y = −11−1
Then, it requires a unit normal field, here taken from the position-vector parametrization
R=sin(φ)cos(θ)sin(φ)sin(θ)cos(φ)
as N=Rφ×Rθ = ijkcosφcosθcosφsinθ−sinφ−sinφsinθsinφcosθ0 = sinφ2cosθsinφ2sinθcosφsinφ. For dσ, take
dσ=Rφ×Rθ dA = sinφ dA
Hence,
∇×F·N = −11−1·sinφ2cosθsinφ2sinθcosφsinφ = sinφ sinφsinθ−sinφcosθ−cosφ
and
∫02 π∫0πsin2φ sinφsinθ−sinφcosθ−cosφ ⅆφ ⅆθ = 0
Maple Solution - Interactive
Should the "Clear All and Reset" button in the Task Template be pressed, all the data that has been input to the template will be lost. In that event, the reader should simply re-launch the example to recover the appropriate inputs to the template.
Tools≻Tasks≻Browse: Calculus - Vector≻Integration≻Flux≻3-D≻Through a Sphere
Flux through a Sphere
For the Vector Field:
Select Coordinate SystemCartesian [x,y,z]Cartesian - othercylindricalsphericalbipolarcylindricalbisphericalcardioidalcardioidcylindricalcasscylindricalconicalellcylindricalhypercylindricalinvcasscylindricallogcylindricallogcoshcylindricaloblatespheroidalparaboloidalparacylindricalprolatespheroidalrosecylindricalsixspheretangentcylindricaltangentspheretoroidal
Maple Solution - Coded
Initialize
Install the Student VectorCalculus package.
withStudent:-VectorCalculus:
Set display of vectors with BasisFormat command.
BasisFormatfalse:
Define F with the VectorField command.
F≔VectorFieldz,−x,−y:
Use the Curl and Flux commands to obtain the flux of ∇×F through S
FluxCurlF,Sphere0,0,0,1,output=integral
∫02π∫0π−sinφsinφcosθ−sinφsinθ+cosφⅆφⅆθ
FluxCurlF,Sphere0,0,0,1 = 0
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