The opposition offered by the conductor to the flow of current is called the electrical resistance of the conductor. Its S.I. unit is ohm.
Resistivity of a substance is defined as the resistance offered by a wire of that substance of 1 metre length and 1 square metre cross-sectional area. Resistivity depends only on the material and is independent of dimensions at a given temperature.
Its S.I. unit is ohm-metre.
