ABSTRACT
At the beginning of the book, we introduced the analogy of water flowing on a landscape. We might say that this vector field that guides the water flow has been created by the abundance or the lack of land mass in the cases of hills and valleys, respectively. In the context of electricity, the vector field of electricity, or electric field, is created by the electric charges. Unlike mass, which is always a non-negative quantity, an electric charge may be positive, neutral, or negative. Canonical examples of electric charges are protons, neutrons, and electrons. In many of our analyses, we will often consider a point charge, which occupies a very small region of space, relative to the length scale of the analysis, so for all practical purposes, it is a point in space. Electric charge is measured in the unit of coulomb (C). The opposite charges (positive and negative) attract each other, and the same charges repel each other. Such interactions are mediated through the electric field.
