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## Homework Statement

Hi, I am studying gauss's law via this book below.[/B]

http://faculty.polytechnic.org/cfle...2_web_pdfs_2010/i-Ch14-PCALC--GAUSS'S LAW.pdf

On page 8, and 9, the book describes the shell method of finding the volume of the sphere and then using the area charge density to find the charge.

I tried it a different method:

volume of a sphere is (4/3) * PI * R^3, so I wrote that the volume was (4/3) * PI * (r-R1)^3.

This makes sense to me: I take the volume of the larger sphere and subtract the volume of the smaller sphere with radiuses "r" and "R1" accordingly.

Could anyone please explain to me why my method is wrong, as I got a totally different answer?

Thank you!

## Homework Equations

gauss's law

## The Attempt at a Solution

attempt is recorded above[/B]