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The Divergence Theorem

Computing flux through a closed surface as a triple integral of divergence over the enclosed solid, sidestepping piecewise surface parameterizations.

Active Calculus Multivariable, The Divergence Theorem

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5 exercises

Activity 13.14.3

  1. Find the flux of the vector field F⃗=⟨3x2+y5,5+ez3,z⟩\vF = \langle 3x^2+y^5,5+e^{z^3},z\rangle through the surface of the solid cube QQ in R3\R^3 with −2≤x≤2-2\leq x\leq 2, −2≤y≤2-2\leq y\leq 2, and −2≤z≤2-2\leq z\leq 2.

  2. Find the flux of the vector field G⃗=⟨x3,y3,z3⟩\vG = \langle x^3,y^3,z^3\rangle through surface consisting of the top half of sphere of radius 33 centered at the origin and the disc of radius 33 in the xyxy-plane (centered at the origin).

2.5

Exercise 15

Let QQ be the volume enclosed by x=0x=0, x=1x=1, y=0y=0, y=1y=1, z=0z=0, and z=1z=1. Compute the flux of F⃗=⟨z2−xy,4yz+cos(x/π),exyz⟩\vF = \langle z^2-xy,4yz+cos(x/\pi),e^{xyz} \rangle through each of the six cube faces.

2.5

Exercise 16

Let QQ be the volume given in cylindrical coordinates by 0≤z≤30 \leq z \leq 3, 1≤r≤21 \leq r \leq 2, and 0≤θ<2π0 \leq \theta \lt 2 \pi. Give an example of a vector field with component functions that are linear in xx, yy, and zz such that the flux of the vector field through the boundary of QQ is 17.

2.5

Exercise 17

Let QQ be the volume given in spherical coordinates by 0≤ρ≤30 \leq \rho \leq 3, 0≤ϕ≤π/40\leq \phi \leq \pi/4, and 0≤θ<2π0\leq \theta \lt 2 \pi. Give an example of a vector field with component functions that are not linear or constant such that the flux of the vector field through the boundary of QQ is 25.

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Exercise 18

Calculate the flux of the given vector field F⃗\vF through the surface SS for each situation below by using an appropriate triple integral from the Divergence Theorem.

  1. The vector field F⃗=⟨2x+3sin⁡(yz),−4y+ex2,7z+arctan⁡(y5)\vF = \langle 2x+3\sin(yz),-4y+e^{x^2} , 7z+\arctan(y^5) through the tetrahedron SS with vertices (0,0,0)(0,0,0), (1,0,0)(1,0,0), (0,2,0)(0,2,0), and (0,0,2)(0,0,2).

  2. The vector field F⃗=⟨xy2,yz2,zx2⟩\vF=\langle xy^2,yz^2,zx^2\rangle through SS, the portion of the sphere of radius 33 centered at the origin having x≥0x\geq 0.

2.5

Adapted from Active Calculus Multivariable © 2013–2026 Nicholas Long, Mitchel T. Keller, and Steven Schlicker. Licensed under CC BY-SA 4.0. Source: Active Calculus Multivariable. Imported at revision 692c03c.