At constant temperature, the resistance of a conductor of particular material varies proportionately with the length and inversely with the area of cross section. Therefore, we get from the laws of resistance,
R ∞ L/A, when temperature and material remain the same.
or, R = ρ (L/A)
Here ρ is a constant, the value of which depends on the material of the conductor and its temperature. This constant is called the resistivity or specific resistance of the material at that temperature.
In equation R = ρ (L/A), if L = 1 unit, A = 1 unit, then, ρ = R.
Therefore, at a particular temperature, the resistance of a conductor of unit length and unit cross sectional area is called the specific resistance of that material at that temperature.
At a certain temperature, the resistance of a conductor depends on its physical conditions (e.g. length, cross section etc.). But the resistivity of a conductor depends only on its material. Electrical resistivity (also known as resistivity, specific electrical resistance, or volume resistivity) is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current.