RESISTIVITY

We know factors affecting resistance are Nature of material, temperature, Length of conductor(L)-As length of a conductor increases resistance of conductor also increases. Length is directly proportional to resistance.(Rα L) and Area of cross-section(A)- As area of cross-section increases resistance of conductor decreases. Area of cross-section is inversely proportional to resistance.(R α 1/A)

From above statements,

      R α L/A

      R = a constant × L/A (Constant is the resistivity of material (ρ))

      R = ρ L/A

      ρ = RA/L

SI Unit Resistivity is ohm-meter (Ωm)

RESISTIVITY

From the equation ρ = RA/L, if we take a conductor of unit length (L= 1) and unit area of cross section (A= 1) then 

ρ = R x 1/1

ρ = R

So,Resistivity is the resistance of a material of unit length and unit area of cross-section.

RESISTIVITY OF DIFFERENT MATERIALS