In this section we introduce mathematical formulas and physical relations for the static case in order to get a visual understanding of electric and magnetic field quantities.
Historically it has been known for a long time that electric charges are the origin of electrical phenomena. Charges produce forces upon each other. We distinguish between positive and negative charges. Charges of opposite signs attract each other whereas charges of same sign push each other away. The absolute value of the Coulomb force FC between two point charges1 Q1 and Q2, separated by a distance r, is given by
where ε0 = 8.854 · 10−12 As/(Vm) is the permittivity of free space.
The direction of the Coulomb force is defined by a straight line through both charges (see Figure 2.1a and 2.1b). In the case of three or more charges we can add up the vectors of the forces by the principle of superposition (vector sum in Figure 2.1c).
Charges exist in discrete values (integer values of elementary charge e = 1.602 · 10−19 C). However, in practical (macroscopic) engineering configurations ...