Gauss' Law: Net Electric Field of Two Spheres

[UWGGEOL]

Homework Statement

Two nonconducting spheres, of r1=3.0cm and r2=2.0cm, are placed of an x-axis. They have surface charge densities of +6.0mC/m² and +4.0 mC/m², respectively, on their outside surfaces. The center of sphere r1 is on the origin and the center of sphere r2 is 10 cm away. What is the net electric field at x=2.0 cm?

Homework Equations

E=kq/r²
Area=4pir²

The Attempt at a Solution

I noticed that x=2.0cm falls inside sphere r1 and that the Electric Field inside a sphere due to an outside charge equals 0. I think this is the answer but want to be sure.

 

[astrosona]

I do not think so! because they are non conducting spheres... so we can not ignore the effect of the second sphere, I guess! i will look it up more though...

 

[Goddar]

The field inside a uniformly charged sphere is zero (the field of THIS sphere vanishes), but the field outside a uniformly charged sphere is the same as if all the charge was at its center (we can treat it like a point-charge on most regards)... You should get your answer easily!

 

[UWGGEOL]

Yeah I tried that before you told me and it was pretty easy and good to know the way i thought was right. I got -3.10x10^3 N/C because of the direction of the field