Flux of Vector Field within Sphere: Find Flux of Given Vector Field

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SUMMARY

The discussion focuses on calculating the flux of a vector field \(\vec{G}\) through spheres of varying radii, specifically using the divergence theorem. Given that the divergence of \(\vec{G}\) is 5 for the region \(2 \leq ||\vec{r}|| \leq 14\) and the flux through a sphere of radius 4 is \(20\pi\), the flux through a sphere of radius 12 can be determined by first calculating the volume of the region between the spheres and applying the divergence theorem. The correct approach involves subtracting the flux through the inner sphere from the flux through the outer sphere.

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Homework Statement



Suppose \vec{G} is a vector field with the property that div\vec{G} = 5 for 2 \leq ||\vec{r}|| \leq 14 and that the flux of \vec{G} through the sphere of radius 4 centered at the origin is 20\pi. Find the flux of through the sphere of radius 12 centered at the origin.

Homework Equations


The Attempt at a Solution



what I tried so far is

20\pi \int_0^{2\pi} \int_0^{\pi} \int_0^{12} \rho^2 sin(\phi)d\rho d\phi d\theta

is this wrong
 
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No integration is needed for this problem. The flux through the region 2 < R < 4 is just

5(volume of region 2 < R < 4)

by the divergence theorem. Use this, together with the fact that the flux through 0 < R < 4 is 20π, to find the flux through the region 0 < R < 2.

Can you see how to take it from here?
 
ok so after I got the flux through region 2< r< 4and through 0 < r< 4 I just substract it right?
 
Yes, but in which order are you going to do the subtraction?
 
it's the 0<r<4 - 2<r<4 correct?
 
Correct.
 

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