Write an expression for the resistivity of a metallic conductor showing its variation over a limited range of temperatures.

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The resistivity of a metallic conductor is given by
             
               ρ_T = ρ₀ [1 + α (T – T₀)]
where,
${\mathbf{\rho }}_{\mathbf{t}}$ is the resistivity at temperature T,
ρ₀ be the resistivity at temperature T_0, and
$\mathbf{\alpha }$ be the temperature co-efficient.