what is resistivity in physics

Resistivity is a property of a material that describes the extent to which it opposes the flow of electric current through it/Book%3A_University_Physics_II_-Thermodynamics_Electricity_and_Magnetism(OpenStax)/09%3A_Current_and_Resistance/9.04%3A_Resistivity_and_Resistance). It is a characteristic property of each material and is useful in comparing various materials on the basis of their ability to conduct electric currents. High resistivity designates poor conductors. Resistivity is commonly symbolized by the Greek letter rho, ρ, and is quantitatively equal to the resistance R of a specimen such as a wire, multiplied by its cross-sectional area A, and divided by its length l; ρ = RA/l. The unit of resistance is the ohm, and in the metre-kilogram-second (mks) system, the unit of resistivity is ohm-metre. The value of resistivity depends on the temperature of the material, and tabulations of resistivities usually list values at 20° C. The resistivity of metallic conductors generally increases with a rise in temperature, but the resistivity of semiconductors, such as carbon and silicon, generally decreases with temperature rise. The resistivity of a material is a measure of how strongly it opposes the flow of electrical current, and the symbol for resistivity is the lowercase Greek letter rho, ρ/Book%3A_University_Physics_II_-Thermodynamics_Electricity_and_Magnetism(OpenStax)/09%3A_Current_and_Resistance/9.04%3A_Resistivity_and_Resistance).