# Current and Conductivity 2010-01-04

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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