Conducting Polymers

Resistance

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

 Material Resistivity (ohm m) Temperature coefficient per degree C Silver 1.59 x10^-8 .0061 Copper 1.68 x10^-8 .0068 Aluminum 2.65 x10^-8 .00429 Tungsten 5.6 x10^-8 .0045 Iron 9.71 x10^-8 .00651 Platinum 10.6 x10^-8 .003927 Manganin 48.2 x10^-8 .000002 Mercury 98 x10^-8 .0009 Nichrome (Ni,Fe,Cr alloy) 100 x10^-8 .0004 Carbon* (graphite) 3-60 x10^-5 -.0005 Germanium* 1-500 x10^-3 -.05 Silicon* 0.1-60 ... -.07 Glass 1-1000 x10^9 ... Hard rubber 1-100 x10^13 ...

*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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