3
Fundamentals of Electric Capacitors
both positive and negative electric charges exist in all physical objects in
the universe whether they are animate or inanimate. A physical object will
display a neutral charge when there are equal numbers of positive charges
(protons) and negative charges (electrons). However, a net electric charge
can occur through unbalancing the charge equilibrium in some areas of an
object. Thus some areas will have more negative than positive charges and
vice versa.
In general, two positive charges reciprocally repel each other as do two
negative charges; while opposite charges feel mutual attractive forces.
Figure 1.2 shows positive and negative charges. Coulomb’s law states that
the electrostatic force between two charges can be described by
q q
( − − ) q q
+
+
F =
= −
−
4πε 0 r
2
4πε 0 r
2
(1.1)
FIGURE 1.2
Field lines of force radiating outward from a positive charge or inward toward a negative
charge.