Temperature has a significant effect on the resistance
of any electrical element. There are three types of electrical substance:
0 1.
Conductors,
0 2.
Semiconductors, and
0 3.
Insulators.
Conductors: In metals or in any good conductor there are
many free electrons. Actually for these free electrons electron flow can occur
and conduction of current happens. But when we heat a conductor or raise its
temperature the molecules of the conductors start to move and vibrate at a much
higher rate than before. So the free movements of the free electrons are hampered
and current cannot pass as easily as before. Thus the resistance of the
conductor increases. In summary:
Increase in temperature will increase the
resistance of a conductor. Therefore conductors have a positive temperature
coefficient.
 |
| Conductors have a positive temperature coefficient |
Semiconductors:
In semiconductors like silicon increase in temperature will help to increase
the number of free electrons or carriers. So increase in temperature will decrease the resistance of the
semiconductor. Therefore they have a negative temperature coefficient.
 |
| Semiconductors and insulators have negative temperature coefficient |
Insulators: In insulator there is no or very less number of
free electrons. Increase in temperature will help some of the electrons to get
free from their outer shell and conduct electricity. So increase in temperature of an insulator will decrease its resistance.
Thus it has a negative temperature coefficient.
