06 February, 2007

Resistance and Conductance

Resistance and Conductance :
Resistance is the opposition of a body or substance to current passing through it, resulting in a change of electrical energy into heat or another form of energy.The electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electri current whichflows through it.Resistance is measured in Ohms denoted by
If the resistance is constant over a considerable range of voltage, then Ohm's Law , I = V/R, can be used to predict the behavior of the material. Although the definition above involves DC current and voltage, the same definition holds for the AC application of resistors.
Whether or not a material obeys Ohm's law, its resistance can be described in terms of its bulk resistivity. The resistivity, and thus the resistance, is temperature dependent. Over sizable ranges of temperature, this temperature dependence can be predicted from a temperature coefficient of resistance. The dependence on resistivity is given by equation
where is called temperature coefficient of resistance.

Conductance :
Conductance is measure of a material's ability to conduct electric charge; the reciprocal of the resistance.Conductance is a positive quantity. The units of conductance are called siemens or mhos. It is denoted by


The conductance of a resistor R is given by equation

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