The specific resistance (resistivity) of a metallic conductor nearly increases with increasing temperature as shown in figure. This is because, with the increases in temperature the ions of the conductor vibrate with greater amplitude, and the collision between electrons and ions become more frequent, over all small temperature range (up to 100ºC). The resistivity of a metal can be represented approximately by the equation

ρ t = ρ 0 (1 + αt)

The factor α is called the temperature coefficient of resistivity.