Question

Why does resistance of a metallic conductor increases with increase of temperature?

Answer 1

Since ρ α 1/τ i.e., the resistivity of the material of conductor is inversely proportional to the average relaxation time (τ) of the free electrons in the conductor. Since the value of τ depends upon temperature of the conductor. That's why with increase in temperature of metal conductor, τ decreases, hence its resistance increases as ρ increases as R is given by R= $\frac{l}{A}$ρ.