Multivariable Calculus · free preview

The Divergence Theorem

Flux out of a closed surface as the triple integral of divergence, sources and sinks as the physical reading, and the lid trick made into a theorem.

1. The third fundamental theorem

The third fundamental theorem

2. A worked cube

A worked cube

3. The radial field, revisited with power

The radial field, revisited with power

4. Capping an open surface

Capping an open surface

5. The theorem's hypothesis

A student replaces the flux integral over an open bowl by a triple integral of divergence over the solid beneath it. What is missing?

6. Shape independence

F=(x,y,z)\mathbf{F} = (x, y, z) and a solid has volume 1010. What is the flux out of its boundary, whatever the shape?

7. Reading divergence physically

A field has divergence −2-2 throughout a region. What does flux out of the region's boundary report?

8. Cube flux

F=(x2,y2,z2)\mathbf{F} = (x^2, y^2, z^2) over the unit cube. Give the total outward flux, as a plain number.

9. Bowl with a lid

The paraboloid z=x2+y2z = x^2 + y^2 below z=1z = 1, with F=(x,y,z)\mathbf{F} = (x, y, z), is capped by the disk at z=1z = 1. The closed flux is 3π/23\pi/2 and the lid's flux is π\pi. Give the bowl's outward flux, in the form a*pi/b.

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