By measuring the resistance of:
(a) various lengths of wire of the same thickness and made of a given material;
(b) several wires of equal length but different areas of cross-section also of the same material;
we may verify the relations (1) and (2) above.
From this expression we see that the resistivity of a material is expressed in ohm metre units and is numerically equal to the resistance of a conductor made of the material of length 1 metre and area of cross-section 1 metre-,
We talked in terms of ohms and metres in the foregoing discussion from which we see that the SI unit of resistivity is the ohm metre (0 m). The sub-unit, ohm centimetre (0 em) is often used especially when dealing with wires of small diameter.