What is resistivity? How does it depend on material, and how does temperature change the resistivity of conductors and semiconductors?

Solution & explanation

For a uniform wire ρ = RA/L. At specified temperature it characterises material, unlike R which also depends on geometry. Metals generally gain resistivity with heating due to scattering. In an intrinsic semiconductor, heating can create more carriers and decrease resistivity; details depend on doping and temperature range.