How does the resistivity of a material depend on temperature? Write the empirical formula.

(N/A) The resistivity of a material depends on its temperature. Different materials exhibit different temperature dependencies.
For metals,the resistivity increases with an increase in temperature.
For semiconductors,the resistivity decreases with an increase in temperature.
Over a limited range of temperature that is not too large,the resistivity of a metallic conductor is approximately given by the empirical formula:
$\rho_{T} = \rho_{0} [1 + \alpha (T - T_{0})]$
Where:
$\rho_{T}$ = resistivity at temperature $T$
$\rho_{0}$ = resistivity at reference temperature $T_{0}$
$\alpha$ = temperature coefficient of resistivity
The unit of $\alpha$ is $(^{\circ}C)^{-1}$ or $(K)^{-1}$.
For metals,the value of $\alpha$ is positive,whereas for semiconductors,$\alpha$ is negative.