<P>Now, this was really strange to witness. After all, none of these =
objects=20
were visibly altered by the rubbing, yet they definitely behaved =
differently=20
than before they were rubbed. Whatever change took place to make these =
materials=20
attract or repel one another was invisible. </P><A=20
name=3D"Charge, early definition"></A>
<P>Some experimenters speculated that invisible "fluids" were being =
transferred=20
from one object to another during the process of rubbing, and that these =

"fluids" were able to effect a physical force over a distance. Charles =
Dufay was=20
one the early experimenters who demonstrated that there were definitely =
two=20
different types of changes wrought by rubbing certain pairs of objects =
together.=20
The fact that there was more than one type of change manifested in these =

materials was evident by the fact that there were two types of forces =
produced:=20
<I>attraction</I> and <I>repulsion</I>. The hypothetical fluid transfer =
became=20
known as a <I>charge</I>. </P>
<P>One pioneering researcher, Benjamin Franklin, came to the conclusion =
that=20
there was only one fluid exchanged between rubbed objects, and that the =
two=20
different "charges" were nothing more than either an excess or a =
deficiency of=20
that one fluid. After experimenting with wax and wool, Franklin =
suggested that=20
the coarse wool removed some of this invisible fluid from the smooth =
wax,=20
causing an excess of fluid on the wool and a deficiency of fluid on the =
wax. The=20
resulting disparity in fluid content between the wool and wax would then =
cause=20
an attractive force, as the fluid tried to regain its former balance =
between the=20
two materials. </P>
<P>Postulating the existence of a single "fluid" that was either gained =
or lost=20
through rubbing accounted best for the observed behavior: that all these =

materials fell neatly into one of two categories when rubbed, and most=20
importantly, that the two active materials rubbed against each other =
<I>always=20
fell into opposing categories</I> as evidenced by their invariable =
attraction to=20
one another. In other words, there was never a time where two materials =
rubbed=20
against each other <I>both</I> became either positive or negative. </P>
<P>Following Franklin's speculation of the wool rubbing something off of =
the=20
wax, the type of charge that was associated with rubbed wax became known =
as=20
"negative" (because it was supposed to have a deficiency of fluid) while =
the=20
type of charge associated with the rubbing wool became known as =
"positive"=20
(because it was supposed to have an excess of fluid). Little did he know =
that=20
his innocent conjecture would cause much confusion for students of =
electricity=20
in the future! </P><A name=3DCoulomb></A><A name=3D"Unit, coulomb"></A>
<P>Precise measurements of electrical charge were carried out by the =
French=20
physicist Charles Coulomb in the 1780's using a device called a =
<I>torsional=20
balance</I> measuring the force generated between two electrically =
charged=20
objects. The results of Coulomb's work led to the development of a unit =
of=20
electrical charge named in his honor, the <I>coulomb</I>. If two "point" =
objects=20
(hypothetical objects having no appreciable surface area) were equally =
charged=20
to a measure of 1 coulomb, and placed 1 meter (approximately 1 yard) =
apart, they=20
would generate a force of about 9 billion newtons (approximately 2 =
billion=20
pounds), either attracting or repelling depending on the types of =
charges=20
involved. </P><A name=3DElectron></A><A name=3DAtom></A><A =
name=3DParticle></A><A=20
name=3DProton></A><A name=3DNeutron></A><A name=3D"Atomic =
structure"></A>
<P>It was discovered much later that this "fluid" was actually composed =
of=20
extremely small bits of matter called <I>electrons</I>, so named in =
honor of the=20
ancient Greek word for amber: another material exhibiting charged =
properties=20
when rubbed with cloth. Experimentation has since revealed that all =
objects are=20
composed of extremely small "building-blocks" known as <I>atoms</I>, and =
that=20
these atoms are in turn composed of smaller components known as=20
<I>particles</I>. The three fundamental particles comprising most atoms =
are=20
called <I>protons</I>, <I>neutrons</I> and <I>electrons</I>. Whilst the =
majority=20
of atoms have a combination of protons, neutrons, and electrons, not all =
atoms=20
have neutrons; an example is the protium isotope =
(<SUB>1</SUB>H<SUP>1</SUP>) of=20
hydrogen (Hydrogen-1) which is the lightest and most common form of =
hydrogen=20
which only has one proton and one electron. Atoms are far too small to =
be seen,=20
but if we could look at one, it might appear something like this: </P>
<P><IMG src=3D"http://sub.allaboutcircuits.com/images/00006.png"> </P>
<P>Even though each atom in a piece of material tends to hold together =
as a=20
unit, there's actually a lot of empty space between the electrons and =
the=20
cluster of protons and neutrons residing in the middle. </P><A =
name=3DNucleus></A>
<P>This crude model is that of the element carbon, with six protons, six =

neutrons, and six electrons. In any atom, the protons and neutrons are =
very=20
tightly bound together, which is an important quality. The tightly-bound =
clump=20
of protons and neutrons in the center of the atom is called the =
<I>nucleus</I>,=20
and the number of protons in an atom's nucleus determines its elemental=20
identity: change the number of protons in an atom's nucleus, and you =
change the=20
type of atom that it is. In fact, if you could remove three protons from =
the=20
nucleus of an atom of lead, you will have achieved the old alchemists' =
dream of=20
producing an atom of gold! The tight binding of protons in the nucleus =
is=20
responsible for the stable identity of chemical elements, and the =
failure of=20
alchemists to achieve their dream. </P><A name=3DRadioactivity></A>
<P>Neutrons are much less influential on the chemical character and =
identity of=20
an atom than protons, although they are just as hard to add to or remove =
from=20
the nucleus, being so tightly bound. If neutrons are added or gained, =
the atom=20
will still retain the same chemical identity, but its mass will change =
slightly=20
and it may acquire strange <I>nuclear</I> properties such as =
radioactivity. </P>
<P>However, electrons have significantly more freedom to move around in =
an atom=20
than either protons or neutrons. In fact, they can be knocked out of =
their=20
respective positions (even leaving the atom entirely!) by far less =
energy than=20
what it takes to dislodge particles in the nucleus. If this happens, the =
atom=20
still retains its chemical identity, but an important imbalance occurs.=20
Electrons and protons are unique in the fact that they are attracted to =
one=20
another over a distance. It is this attraction over distance which =
causes the=20
attraction between rubbed objects, where electrons are moved away from =
their=20
original atoms to reside around atoms of another object. </P><A=20
name=3D"Strong nuclear force"></A>
<P>Electrons tend to repel other electrons over a distance, as do =
protons with=20
other protons. The only reason protons bind together in the nucleus of =
an atom=20
is because of a much stronger force called the <I>strong nuclear =
force</I> which=20
has effect only under very short distances. Because of this =
attraction/repulsion=20
behavior between individual particles, electrons and protons are said to =
have=20
opposite electric charges. That is, each electron has a negative charge, =
and=20
each proton a positive charge. In equal numbers within an atom, they =
counteract=20
each other's presence so that the net charge within the atom is zero. =
This is=20
why the picture of a carbon atom had six electrons: to balance out the =
electric=20
charge of the six protons in the nucleus. If electrons leave or extra =
electrons=20
arrive, the atom's net electric charge will be imbalanced, leaving the =
atom=20
"charged" as a whole, causing it to interact with charged particles and =
other=20
charged atoms nearby. Neutrons are neither attracted to or repelled by=20
electrons, protons, or even other neutrons, and are consequently =
categorized as=20
having no charge at all. </P><A name=3DCoulomb></A><A name=3D"Unit, =
coulomb"></A><A=20
name=3D"Charge, modern definition"></A><A name=3D"Charge, =
elementary"></A><A=20
name=3D"Elementary charge"></A>
<P>The process of electrons arriving or leaving is exactly what happens =
when=20
certain combinations of materials are rubbed together: electrons from =
the atoms=20
of one material are forced by the rubbing to leave their respective =
atoms and=20
transfer over to the atoms of the other material. In other words, =
electrons=20
comprise the "fluid" hypothesized by Benjamin Franklin. The operational=20
definition of a coulomb as the unit of electrical charge (in terms of =
force=20
generated between point charges) was found to be equal to an excess or=20
deficiency of about 6,250,000,000,000,000,000 electrons. Or, stated in =
reverse=20
terms, one electron has a charge of about 0.00000000000000000016 =
coulombs. Being=20
that one electron is the smallest known carrier of electric charge, this =
last=20
figure of charge for the electron is defined as the <I>elementary =
charge</I>.=20
</P><A name=3D"Static electricity"></A><A name=3D"Charge, =
negative"></A><A=20
name=3D"Charge, positive"></A><A name=3D"Negative charge"></A><A=20
name=3D"Positive charge"></A>
<P>The result of an imbalance of this "fluid" (electrons) between =
objects is=20
called <I>static electricity</I>. It is called "static" because the =
displaced=20
electrons tend to remain stationary after being moved from one =
insulating=20
material to another. In the case of wax and wool, it was determined =
through=20
further experimentation that electrons in the wool actually transferred =
to the=20
atoms in the wax, which is exactly opposite of Franklin's conjecture! In =
honor=20
of Franklin's designation of the wax's charge being "negative" and the =
wool's=20
charge being "positive," electrons are said to have a "negative" =
charging=20
influence. Thus, an object whose atoms have received a surplus of =
electrons is=20
said to be <I>negatively</I> charged, while an object whose atoms are =
lacking=20
electrons is said to be <I>positively</I> charged, as confusing as these =

designations may seem. By the time the true nature of electric "fluid" =
was=20
discovered, Franklin's nomenclature of electric charge was too well =