Using the formula from section 1.2, when temperature rises to 70°C, the resistivity of copper wire increases by about 20%. This means the current carrying capacity of the conductor is significantly reduced. The temperature affects the dimensions of the conductor; a higher temperature causes an expansion in a material while a colder temperature causes a contraction. And with this expansion/contraction a change in resistance occurs as a thicker wire has less resistance to current flow than a thinner one. Higher temperatures mean more energy and more motion. In contrast, cold means slow moving molecules. A conductor has low electrical resistance when hot and higher electrical resistance when cold. This is due to the increased thermal agitation of electrons in the conductor when it is. In metals, higher temperatures cause atoms to vibrate more, which makes it harder for electrons to flow through the lattice. That increased scattering of electrons raises resistance. Checking the voltage/current (V/I) ratio of conductors at various temperatures shows that the resistance of most conducting materials increases linearly with temperature except at very hot or very cold temperatures. The resistance of the conductor increases with an increase in temperature, while the resistance of insulators and semiconductors decreases with an increase in temperature. At high temperatures, atoms will vibrate more vigorously than they would at room temperature. Conversely, atoms vibrate less at colder temperatures. In a conductor like copper, these vibrations can cause resistance for flowing electrons. Although the resistance of a conductor changes with the size of the conductor (e.g. thicker wires have less resistance to current flow than thinner wires), the resistance of a conductor also changes with changing temperature. At its core, resistance (measured in ohms) rises with temperature because heat energizes the metal’s atomic lattice. For copper and aluminum—the two most common conductor materials—this relationship is nearly linear over typical operating ranges.