Continuous Charge Distribution

So far, every calculation in this chapter has treated charge as concentrated at one or more discrete POINTS. In many real, practical situations, however, a very large number of individual charges are packed extremely close together -- much closer to each other than their overall distance from the point where the resulting field is being calculated. In such cases it becomes far more convenient (and, for all practical purposes, exactly as accurate) to treat the whole collection of charges not as individual points but as a single total charge spread out CONTINUOUSLY -- along a line, over a surface, or throughout a volume -- rather than trying to track every individual point charge separately. …