Define Resistivity of a Material

H1. Define resistivity of a material. Does it depend on temperature?

Answer: 

Resistivity of any material is defined as the electrical resistance offered by a conductor of unit cross sectional area per unit length. 

It can be considered as the characteristic feature of each material and hence, can be used to distinguish different types of materials based on their ability to conduct electricity.

Resistivity is usually represented by the Greek letter rho, ρ, is quantitatively equivalent to the resistance R of a material, for example, a wire, duplicated by its cross-sectional region A, and separated by its length l. 

                                         ρ = RA/l. 

The unit of obstruction is the ohm.

For a good conductor, like hard-drawn copper, at 20° C (68° F) is 1.77 × 10-8 ohmmeter, or 1.77 × 10-6 ohm-centimetre. At the other limit, electrical encasings have resistivities in the range 1012 to 1020 ohmmeters.

Temperature plays an important role while deciding the value of resistivity for any material.

For metallic conductors, the resistivity increases on increasing the temperature. On the other hand, for semiconductors, such as carbon and silicon, the resistivity in this case, decreases with temperature.