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The electrical resistance (and conductance) of a material changes with temperature. For different type of materials, the amount and direction of this change is different (refer to the attached figure).
In case of electrolytes, insulators and semiconductors the resistance of the material decreases with rise in temperature. For semiconductors and insulators, as the temperature increases, some of the electrons acquire energy and become free for conduction. For electrolytes and conducting liquids, an increase in a solution’s temperature of electrolytic solutions (or liquids) will cause a decrease in its viscosity and an increase in the mobility of the ions in solution. An increase in temperature may also cause an increase in the number of ions in solution due to dissociation of molecules. As the conductivity of a solution is dependent on these factors then an increase in the solution’s temperature will lead to an increase in its conductivity.
For metallic conductors, the resistance of all pure materials increases linearly with temperature over a limited range of temperature. As the temperature increases, the ions inside the metal acquire energy and starts oscillating about their mean positions. These vibrating ions collide with the moving electrons. Hence resistance increases with increasing temperature. In case of certain materials, however, the resistance-temperature graph exhibit peculiar characteristics in that below a certain temperature, in the very low temperature region, their resistance falls dramatically to become zero. These materials are called superconductors and the temperature referred to above is the critical temperature for that material.
Conductivity is the reverse of resistivity and exhibits just inverse pattern of variation with temperature.
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