The applet makes the following assumptions:

• The source object, i.e., the object responsible for the existence of the electric field is a perfect sphere of non-zero radius..
• The charge density of the source object is uniform throughout the object.

A consequence of these assumptions is that, for points outside the source, the magnitude of the electric field depends on the distance d of the field point from the center of the source as if the source were a point particle at the center of the source with all of the source charge concentrated on this particle.

For field points outside the source object, the applet therefore simulates the electric field of a point source, which varies with d like 1/d².

The applet does not permit field points inside the finite source object. Its purpose is to simulate the electric field due to a point charge.