Resistivity of the metallic conductor increases with increase in temperature
When we increase the temperature of the metallic conductor,its constituent atoms vibrate with greater amplitudes then usual.This results to the more frequent collison between ions and electrons
As a result average time between the two successive collision decreases resulting the decrease in drift velocity
Thus increase collison with the increase in tempearture results in increase resistivity
For small temperature variations ,resistivity of the most of the metals varies according to the following relations
ρ(T)=ρ(T0)[1 + α(T-T0)] Where ρ(T) and ρ(T0) are the resistivies of the material at temperature T and T0 respectively and α is the constant for given materail and is known as coefficient of resistivity.