Resistance varies depending on which material a voltage is being applied to. Resistance is measured in ohms, W. The resistance is directly related to the characteristics of the conducting material. The resistivity (this is in essence the resistance of the material per unit length) indicates whether or not a material is a conductor or an insulator. For example polymers or plastics have generally high resistivites that means they would be classified as insulators however we know that they are capable of conducting electricity.
Resistivity and Temperature Coefficient at 20 C
*the resistivity of semiconductors like silicon depend strongly on the level of impurities present
The conductivity, s , of a material is therefore the reciprocal of resistivity.
s = 1/r
Electrical Conductivity is an anistropic property, it varies depending on direction i.e. along the material the value is different compared to that when measured in a perpendicular direction.
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