It can be
measured with the help of a Wheatstone bridge with which you are
familiar from your study of physics The electrical resistance of any object
is directly proportional to its length, l, and inversely proportional to its
area of cross section, A That is,
R µ l
A  or R = r l
A
(2 17)
The constant of proportionality, r (Greek, rho), is called resistivity
(specific resistance)