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Problem:

Consider the vector field $F=z\hat{i}+y\hat{j}+x\hat{k}$, and $S$ the unit cube.

unit cube

Find $\int_S\ F\cdot dS$

Solution:

I have used the divergence theorem:

$\iint_S\ \vec{F}\cdot d\vec{S}=\iiint_S\ \text{div}\vec{F}\ dV$

So, for the vector field $F$ the diverge is $1$.

Then the triple integral behaves:

$\int_{0}^{1}\int_{0}^{1}\int_{0}^{1} dxdydz=1$

Does the way I have used the divergence theorem is correct? I think the result is incorrect because the sum of each cube side is greater than 1.

InfZero
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