# Electric field outside of a cavity

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1. Jul 10, 2015

### Domenico94

1. The problem statement, all variables and given/known data

Hi everyone. I m just studying capacitors but I have problems with gauss law. In one exercise it says that we have a sphere(cavity) of radius r, with a charge q placed inside the sphere of it. Wie have to find the electric field inside and outside sphere.
The solution says: inside the sphere the electric field is q/4πeor^2,Outside of it the field is 0.
The thing I don't understand, why is the field 0?shouldn't we have a distribution of charge for which inside the sphere we have a charge -q, so the net field is 0,then on the surface we have a charge +q that gives an electric field,(q/4πr^2),similar to that of a point-like charge??? Please help me

2. Relevant equations

3. The attempt at a solution

2. Jul 10, 2015

### haruspex

Is this a cavity within a conductor, and you are asking about the field outside the cavity but still within the conductor? If not, please provide details exactly as stated in your referenced text.

3. Jul 10, 2015

### rude man

I think you mean inside the cavity, and outside the cavity but still inside the sphere.