Voltage:

        The electric pressure that must be applied to cause electron movement
is called voltage. When such a voltage is applied to a conducting
medium, free electrons move progressively from atom to atom and constitute
what is known as current flow. In electronic and electric practices,
a continuous path for current flow is formed by interconnecting wires,
controls, relays, transformers, transistors, resistors and many other
components to form what are known as circuits. Such circuits serve
many purposes, but they all control, regulate, and harness the flow of
electrons or which is electricity.

        The required voltage neccesary to force current through an electric
circuit may be obtained from many sources. Some of these sources may be
a battery or a generator. There are many types of both, a flashlight 
battery has only one cell which supplies 1.5 volts. If you place more than 
one end to end the voltage is multiplied by the number of batteries. So if
you have a two battery flashlight, the voltage is 3 volts, a 3 cell the
voltage is 4.5 volts and so on. Some batteries have more than one cell
to the battery, your car battery for instance is probably a 12 volt
battery, meaning it has 8 cells of 1.5 volts each.

        There are many types of generators also, from the thermocouple
which is two dissimilar pieces of metal connected together, to the power
plant size generator that supplies voltage to your home and office.

Units of voltage:
        Electrical pressure is needed to move electrons through a conductor
to cause current to flow. Such pressure is known as electromotive force
and is abbreviatedemf. The unit of emf is the volt named
after Alessandro Volta (1745 - 1827) the italian researcher who first
built a cell which provided electromotive force and which was the forerunner
of our modern battery. Either V or E designates voltage (electric pressure),
and sometimes the word Potential is also used. All these terms have
the same meaning. A volt is the quantity of electromotive force that will
cause one ampere of current to flow through one ohm of resistance.

        The source of electrons, from a battery or othe electric generating
devicec, is referred to as the negative terminal or negative section of the
unit. The terminal toward which the electrons flow is designated as the 
positive terminal. Instead of referring to the two different types of
potentials as charges, the term Polarity is used. Thus, a flashlight
cell may have a potential (emf) of 1.5 volts, with one terminal having a 
negative polarity and the other terminal a positive polarity.

        In practicle electrical and electronic applications voltages of a
fractional value will frequently be encountered, as well as voltages having
values up in the thousands, depending on the amount of electric pressure
necessary to force current flow through the resistances encountered in the
various circuits and devices. Fractional unit values of voltage are often
in terms of a millivolt (one thousanth of a volt) or microvolt
(one millionth of a volt). Thus 0.001-V can be expressed as 1 millivolt (1-mV)
while 0.00003-V can be expressed as 30 microvolt. High voltages are often
designated as kilivolts(kV),to indicate thousands of volts. Thus
10 kV indicates 10 thousand volts.

Current and Conductivity:
        A current flow path is provided by wires or other metals and thus
form conductors of electricity. The ability of a substance to 
conduct electric current is termed conductivity. Current can also
flow in substances such as liquids, gases, or materials whose composition
offers opposition to the flow and limits the amount of current to definite
quantities. The unit of electric current is known as the Ampere,
named after Andre' Ampere (1775 - 1836) the famous French expermenter 
and scientist. One ampere of current represents the exact quantity of
electrons that flows past a given point in one second and is equal to one
Coulomb. The symbol for current is the capitol letter I for intensity
or the symbol A for ampere.

        All substances do not provide the same degree of conductivity since
the number of free electrons present depends on the atomic structure of the
substance. Various metals offer different opposition to current flow, with
some providing good conductivity and others opposing current flow to a 
considerable degree. The opposition of a substance to the flow of current
is known as Resistance and the unit of measurement for such resistance
is termed an OHM, in honor of George Ohm (1787 - 1854) the 
German professor who formulated the basic law relating to current flow and
resistance known as Ohm's Law. The symbol for resistance is the 
capitol letter R and the symbol for ohms is the greek Omega symbol.

        The measure of how well a substance will permit current flow is
known as Conductance. Because conductance is functionally opposite
to resistance, it is the reciprocal of resistance and is therfore equal
to the numeral one divided by the value of resistance, as expressed by
the formula I/R. Thus, if a particular resistance is 1000 ohms the 
conductance is one-onethousanth or 0.001. Because conductance is the
opposite of resistance, the unit for conductance is expressed as the word
ohm spelled backwards which is MHO. The conductance of the example
is 0.001 Mho. A fractional measurement of mho is the micromho. This is
one-millionth of a mho. The symbol for mho is or conductance is G.
Top of Page