Before you draw a spherical charge object, you have to create a charge object category on the navigation tree. In [[EM.Ferma]], objects are grouped together and organized by their static behavior under the “Physical Structure” node of the navigation tree. There are several categories to choose from: fixed-potential PEC objects, dielectric/magnetic materials, volume charges, etc. All the objects belonging to the same charge group have the same color and the same charge density.
To create a new charge category, right-click on the '''Volume Charges''' item in the navigation tree and select <b>Insert New Charge Source...</b> from the contextual menu. The New Charge Source dialog opens up with a default name CS_1 and a default purple color. In the section titled "Source Properties", you will see a default value of -1e-5C/m<sup>^3</sup> for '''Charge Density'''. This means a default negative charge. Replace this with a positive value of +1e-8 C/m<sup>^3</sup>. Close the dialog and return to the project workspace (main window). The last object group created in the navigation tree remains as the "Active" group, and its name is displayed in bold letters, meaning that all the objects you draw will belong to this group.
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