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Current and Conductivity

Discussion in 'Electronic Theory' started by ElectroMaster, Jul 19, 2002.

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  1. ElectroMaster

    ElectroMaster Administrator

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    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.
     
  2. luisgerman

    luisgerman New Member

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    Thanks ElectroMaster:

    Something to remark:

    (just for the benefit of the forum users <feasible diverse levels of acquaintance)


    Electrical conductance is the reciprocal of electrical resistance. It is a measure of how easily electricity flows along a certain path through an electrical element. The SI derived unit of conductance is the siemens (formerly referred to as the reciprocal ohm or mho). Oliver Heaviside coined the term in September 1885.

    Electrical conductance should not be confused with conduction, which is the mechanism by which charge flows, or with conductivity, which is a property of a material.

    Electrical conductivity or specific conductivity is a measure of a material's ability to conduct an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current. The conductivity σ is defined as the ratio of the current density to the electric field strength.

    Electrical conduction is the movement of electrically charged particles through a transmission medium (electrical conductor). The movement can form an electric current in response to an electric field. The underlying mechanism for this movement depends on the material.

    Conduction in metals and resistors is well described by Ohm's Law, which states that the current is proportional to the applied electric field. The ease with which current density (current per area) j appears in a material is measured by the conductivity.
     
    Last edited: Feb 2, 2007
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