ELECTRICITY, MAGNETS, AND CIRCUITS
Section I. INTRODUCTION
LAW OF ELECTROSTATICS
a. Like charges repel each other; unlike charges attract each other--this is the
fundamental law of electricity. This attraction or repulsion is mutual and is easily
demonstrated (figure 2-1). If two bodies are negatively (or positively) charged, they
repel each other and remain separated. If one is negatively charged and the other is
positively charged, they attract each other. The force of attraction (or repulsion)
between two charged particles is directly proportional to the product of their charges
and inversely proportional to the square of the distance between them.
Figure 2-1. Like charges repel; unlike charges attract.
b. Since the positively charged ion is so much heavier and larger than the free
electron, positive charges are less mobile than the lighter, negatively charged electrons.
Usually only negative charges (electrons) move in a solid conductor; consequently, only
negative charges move through wire. The electrons in the valence (outer) orbits, called
"free" electrons, are not tightly bound to the atom; these are the ones that may move
freely from atom to atom.
a. Electric current indicates electric charges in motion. Dynamics deals with
bodies in motion. The science of electricity in motion is known as electrodynamics.
b. In general, all materials may be divided into two major categories--conductors
and nonconductors (insulators). A material's atomic structure determines its
conductivity. Materials allowing electrons to flow with comparative freedom are
conductors; those not allowing electrons to flow freely are nonconductors or insulators.
Since materials have varying degrees of conductivity, there are no perfect conductors or