Question

As if we raise the temperature,resistance increases in pure metals.But manganin,nichrome and constantan are not affected by temperature.Nichrome is used in electrical irons.It has high resistance but how can we say that due to its high resistance it becomes red hot as it is not affected by temperature

Answer 1

Metals, including alloys, have free electrons as charge carriers. Their movement controls by defects. One of defects of usual metal is oscillations of atoms due to temperature. More temperature - more oscillations - more collisions of electrons with atoms - less mobility - more resistivity. In alloys, like constantan, atoms are in disorder so alloys have big resistivity. Their additional disorder due to temperature increase is insignificant. That is why alloys have no temperature dependence of resistivity. The same picture is with metal glasses.