$18\mathrm{.}1($a$)$ Compute the electrical conductivity of cylindrical silicon specimen $5\mathrm{.}1$ mm $(0\mathrm{.}2$ in$.)$ in diameter and $51$ mm $(2$ in$.)$ in length in which a current of $0\mathrm{.}1$ A passes in an axial direction. A voltage of $12\mathrm{.}5$ V is measured across two probes that are separated by $38$ mm $(1\mathrm{.}5$ in$.).($b$)$ Compute the resistance over the entire $51$ mm $(2$ in$.)$ of the specimen.