At a particular temperature, the resistance (R) of a conductor of uniform cross section is
i. directly proportional to its length (l),
i.e., R ∝ l ……….. (1)
ii. inversely proportional to its area of cross section (A),
R ∝ \(\frac{1}{A}\) ……….. (1)
From equations (1) and (2),
R = ρ\(\frac{l}{A}\)
where ρ is a constant of proportionality and it is called specific resistance or resistivity of the material of the conductor at a given temperature.
iii. Thus, resistivity is given by,
ρ = \(\frac{RA}{l}\)
