Formally, as we will see later in
this
course, the unit of electric current - the Ampere - is the
defined
unit, one of the seven basic units (meters, kilograms, seconds,
amperes, temperature, candela, mole). The Coulomb is then
defined
as Ampere.Seconds. However, in developing the basic theory
of
electricity it is more convenient to "pretend" that the Coulomb
is the
basic unit; the Ampere is then Coulomb/sec. Electric
charge is "quantized"
in
units of the charge on the electron, e = 1.6 x 10-19
C. That is charge always appears in integer multiples of
"e". Unless we are dealing with individual atoms or
sub-atomic
particles, since the value of "e" is so small, this quantization
is not
apparent and need to be considered. 
Conservation of charge 
"The net electric charge of an isolated system
is
constant"
However, Note that in calculating
the net charge
the sign of
the charges must be taken into account, e.g. the net charge of a
system
containing objects with +2 C and -1 C is +1 C.
The conservation of charge is a basic physical "law" in the same manner as mass, energy and momentum conservation.
"Like charges repel - unlike charges attract"
"If
I
were
as
rich
as
Rockerfeller, I'd be richer than
Rockerfeller"
"How's that?"
"I'd do a bit of window cleaning on the side"
Dr. C. L. Davis
Physics Department
University of Louisville
email: c.l.davis@louisville.edu
