Current and Conductivity:

Current:

        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.
Kirchoff's Laws:
	
	Gustav Kirchhoff (1824 - 1887>, The German scientist, formulated two
important laws concerning electric circuits. These ar known as Kirchoff's
Lawsand may be stated as follows:

	1. The current (or sum of currents) flowing into any junction of
	   an electric circuit is equal to the current (or sum of currents)
           flowing out of that junction.
 	2. The power source voltage (or sum of such voltages) around any
	   closed circuit is equal to the sum of the voltage drops across
	   the resistances around the same circuit.


Conductance:
        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.

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