Define resistance or specific resistance and write a note on it.

(N/A) The electrical resistance of any object is directly proportional to its length $l$ and inversely proportional to its area of cross-section $A$.
$R \propto \frac{l}{A}$
$\therefore R = \rho \left( \frac{l}{A} \right)$ and $\rho = R \left( \frac{A}{l} \right)$
Here,$\rho$ (rho) is the specific resistance or resistivity.
Unit: The $SI$ unit of resistivity is ohm meter $(\Omega \ m)$,and sometimes it is expressed as ohm centimetre $(\Omega \ cm)$.
Note: $IUPAC$ recommends the use of the term resistivity over specific resistance.
If $l = 1 \ m$ and $A = 1 \ m^2$,then $R = \rho$.
$SI \ unit \ of \ \rho = \frac{(\Omega)(m)^2}{m} = \Omega \ m$.
Conversion: $1 \ \Omega \ m = 100 \ \Omega \ cm$ and $1 \ \Omega \ cm = 0.01 \ \Omega \ m$.