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## Homework Statement

A hollow insulating sphere with an inner radius of 6.58 cm and outer radius of 11.7 cm has a uniform charge density of 79.9 μC/m3 distributed throughout the volume between.

If we want to use Gauss' Law to find the electric field at r = 17.2 cm, what "charge enclosed" should we use?

## Homework Equations

RHO = Q/V

a = .0658 m

b = .1170 m

r = .1720 m

therefore r > b > a

## The Attempt at a Solution

i kno RHO = Q/V

i just don't kno what V to use

i've used v = 4/3(pi)(.1720^3)

i've used v = (4/3)(pi)(.1720^3 - .1170^3)

think i've used every combination of r

i kno i'm overlooking something incredibly simple

blah!