In this topic, you study the temperature coefficient of resistance. And effects of temperature on the resistance.
The temperature coefficient of the resistance is defined as the change in resistance per ohm per degree rise in temperature. It is denoted by letter and the unit is per degree centigrade. The value of temperature coefficient Of resistance for copper is 0.0043 per degree. Let there by any resistance which has got the following values:
Ro Resistance at OOC in Ohm
R, Resistance at toc in ohm
t Rise in temperature in oc
The temperature coefficient.
Now when the temperature is raised from OOC to IOC the change in :esistance is from RO to Rt.
so the change in resistance (R, — RO) Q.
So according to the definition, the change in resistance per ohm per degree rise of temperature i.e.,
Change in resistance
Temperature coefficient
Effects of temperature
The effect of the temperature on the resistances of various materials is as follows:
(i) Most conductors. The resistance increases with the increasing of the temperature
R Temperature
for example, copper, silver, aluminium etc.
l. With pure metals. The resistance increases regularly with the increasing of the temperature.
2. With alloys. The resistance increases slightly with the increasing of temperature but not regular.
3. With partial conductors. The resistance decreases with the increasing of the temperature as in case of carbon. The hot resistance of carbon is less then the cold resistance.
(ii) With insulators. With the increasing of temperature, the resistance of the insulator decreases. The resistances which are perfect insulator at normal temperature, may become conductor when hot. The temperature coefficient of carbon is negative.
(iii) With electrolyte. The resistance of the electrolyte decreases with the increasing of temperature and resistance increases with the decreasing of the temperature, so an electrolyte has more resistance when cold and less when hot. It has negative temperature coefficient.