Temperature has a significant effect on the resistance of conductors,
semiconductors, and insulators.
Effect on Conductors
Conductors have a generous number of free electrons, and any introduction
of thermal energy will have little impact on the total number of free
carriers. In fact, the thermal energy only increases the intensity of the
random motion of the particles within the material and makes it increasingly
difficult for a general drift of electrons in any one direction to be
established. The result is that
for good conductors, an increase in temperature results in an
increase in the resistance level. Consequently, conductors have a
positive temperature coefficient.
The plot in Fig. no.1 has a positive temperature coefficient.
Fig.no.1: Effect of temperature on the resistance of copper.
Effect on Semiconductors
In semiconductors, an increase in temperature imparts a measure of thermal
energy to the system that results in an increase in the number of free
carriers in the material for conduction. The result is that
for semiconductor materials, an increase in temperature results in a
decrease in the resistance level. Consequently, semiconductors have
negative temperature coefficients.
Effect on Insulators
As with semiconductors, an increase in temperature results in a
decrease in the resistance of an insulator. The result is a negative