The resistance of all pure metallic conductors increase with increase in temperature
Resistance of a pure metal is plotted against different temperatures. Say for temperature T1, value of resistance is R1
For temperature T2, value of resistance is R2. And for temperature T3, value of resistance is R3
It is found that over a range of temperature, the graph is practically a straight line
If this straight line is extended, it cuts the temperature axis at some temperature minus
T0 degree centigrade. This temperature is known as inferred zero resistance temperature
Inferred zero resistance temperature, as shown in the graph, is temperature at which
the resistance of the conductor becomes zero. But in practice, at this temperature, the resistance of the metal has some non-zero
value, as because the rate of decrease of resistance with decreasing temperature does
not remain constant for all ranges of temperature. From the graph it is found that R2 by R1 is equal to T0 plus T2 divided by T0 plus
T1 if we apply the similarity triangles. Resistance of the metal conductor can be calculated at any temperature by using this equation
if R1 is known at T1 and also inferred zero resistance temperature is known for that metal conductor
The variation of resistance with temperature is often used to determine the temperature
variation of an electrical machine during its operation. Let's take an example of testing an electrical motor
First, resistance of the coil in the motor is taken before and after the test run
From increase in resistance during the test, one can easily determine the rise of temperature
of coil during the test. Thank You