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## Homework Statement

a spherical shell has an outer radius R and a inner radius R/2 and carries a total charge -q, distributed with uniform charge density. A point charge +q is at the centre of the sphere. Calculate the electric field strength for R/2<r<R

## Homework Equations

Gauss' Law

## The Attempt at a Solution

I figured out the charge density in the shell ρ = [itex]\frac{-6q}{7πR^3}[/itex], so the charge enclosed by a gaussian sphere is q(1-[itex]\frac{8r^3}{7R^3}[/itex])

Then using gauss' law I get E = [itex]\frac{q}{4πε_0r^2}[/itex](1-[itex]\frac{8r^3}{7R^3}[/itex])

But my book says E = [itex]\frac{q}{4πε_0r^2}[/itex][itex]\frac{8}{7}[/itex](1-[itex]\frac{r^3}{R^3}[/itex])

Also does anyone know why the latex things aren't working? I'm new to all this stuff.

Edit: cheers guys

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