17)
The constant of proportionality, r (Greek, rho), is called resistivity
(specific resistance) Its SI units are ohm metre (W m) and quite often
its submultiple, ohm centimetre (W cm) is also used IUPAC recommends
the use of the term resistivity over specific resistance and hence in the
rest of the book we shall use the term resistivity Physically, the resistivity
for a substance is its resistance when it is one metre long and its area
of cross section is one m2