A couple of months ago Paul Tonkinson mentioned how you can't simulate the field inside a sphere in the 2D PhET simuation. Geogebra is 3D so I thought I'd give it a go. It took some time to work out how to do it but here it is. I only used 6 charges so the field doesn't cancel everywhere inside but you get the idea. The length of each vector is given by the radius of a sphere centred on the red point. The radius of the sphere is proportional to the distance of the red point from the charge, this is given by the length of a line segment (hidden). If anyone wants to make a simulation with a sphere covered in points then go ahead, and please share it :-)