When does the electric field equal 0 in Gaussian surface-type questions?

[pcml100]

Homework Statement

When asked for the electric field in flux and guassian surface-type questions I'm getting confused as to when the elecrtic field = 0.

I thought that whenever I had a Gaussian surface (sphere, cylinder, box, etc), the electric field inside it would be 0, but I'm seeing that in some cases it's not. I just don't understand...

I'd appreciate any input. thanks

 

[madmike159]

There is a graph on this page

http://www.phys.uri.edu/~gerhard/PHY204/tsl56.pdf

The E field is 0 at the very center, maximum at the surface and 0 infinatly far away.

If a object is not a sphear or not uniformly charged there may be parts which have no E field through them.

 

[ideasrule]

A Gaussian surface is just a surface you make up because it's convenient for your calculations. There's no reason why a random surface that you chose has to have 0 electric field. In fact, in most cases we choose a surface with constant non-zero electric field, because then it would be easy to solve for that field.