What is temperature coefficient of resistance? Temperature coefficient of resistance is the measure of change in electrical resistance of any substance per degree of temperature change. As I wrote in the page under title resistance variation with temperature that electrical resistance of every substance changes with change in its temperature.
In electrical engineering or in electronics, we know that resistance of a wire or a conductor changes with temperature. Although, it is desired that resistance should remain constant and it should be independent of the temperature. Thus, the change of resistance per degree change in temperature is called Temperature Coefficient of resistance, normally it is represented by a symbol Alpha.
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- 1 What is Temperature Coefficient of Resistance?
What is Temperature Coefficient of Resistance?
For pure metals, it is positive, means the resistance increases with temperature. For the elements like carbon, silicon, and germanium, this coefficient is negative, means the resistance decreases with increasing temperature. Thus, to make highly precise resistances where resistance does not change alloys are required.
Let us take a conductor having a resistance of R0 at 0oC and Rt at toC respectively. From the equation of resistance variation with temperature we get
This αo is called temperature coefficient of resistance of that substance at 0oC. From the above equation, it is clear that the change in electrical resistance of any substance due to temperature mainly depends upon three factors –
- the value of resistance at initial temperature,
- the rise of temperature and
- the temperature coefficient of resistance αo.
This αo is different for different materials, so effect on resistance at different temperature are different in different materials.
So the temperature coefficient of resistance at 0oC of any substance is the reciprocal of the inferred zero resistance temperature of that substance. So far we have discussed the materials that resistance increases with increase in temperature, but there are many materials electrical resistance of which decreases with a decrease in temperature.
Actually in metal if the temperature increases, the random motion of free electrons and interatomic vibration inside the metal increase which result in more collisions.
More collisions resist the smooth flow of electrons through the metal, hence the resistance of the metal increases with the rise in temperature. So, we consider the temperature coefficient of resistance as positive for metal.
How Does Resistance Change With Temperature
Temperature co-efficient refers the change of resistance with respect to temperature of a substance. If it’s resistance increased with temperature, then the characteristics of the substance is called as positive temperature coefficient.
For example: any metallic conductor (Cu, Fe). On the other hand if it’s resistance decreased with temperature, then the characteristics of the substance is called as negative temperature coefficient. For example: insulators and semiconductors.
Otherwise, If it’s resistance doesn’t vary with temperature, then the characteristics of substance is called as zero temperature coefficient. Actually there is no absolute zero temperature coefficient substance. But resistance of materials like eureka, manganin, constantan etc. have changed negligible (almost zero) with temperature.
Review the Concept of Temperature Coefficient of Resistance
The electrical resistance of conductors such as silver, copper, gold, aluminum, etc., depends upon collision process of electrons within the material.
As the temperature increases, this electron collision process becomes faster, which results in increased resistance with the rise in temperature of the conductor.
The resistance of conductors generally rise with rise in temperature. If a conductor is having R1 resistance at t1oC and after raising the temperature, its resistance becomes R2 at t2oC. This rise in resistance (R2 – R1) with rise in temperature (t2 – t1) depends on following things –
By combining above effects,
Where, α is the temperature coefficient of resistance of material at t1oC. From Equation (1)
Temperature Coefficient of Resistance of Copper
The Temperature Coefficient of Copper (near room temperature) is +0.393 percent per degree C. This means if the temperature increases 1°C, the resistance will increase 0.393%.
You have 100 feet of 20 gauge wire and its resistance is 1.015 ohms at 20° C (room temp). If the temperature of the wire goes up 10°C, the resistance will change by 0.0399 ohms (10 degrees * 0.00393 per degree * 1.015 ohms = 0.0399 ohms).
The wire resistance will now be 1.015 ohms + 0.0399 ohms = 1.0549 ohms.
You have 1 foot of ribbon cable with a resistance of 0.0649 ohms at 20 degrees C. You plug the wire into your cable tester and keep your hands on the wire while it tests. The wire temperature goes up 10°C because of your body heat. The wire resistance will go up 0.00255 ohms (10 degrees * 0.00393 per degree * 0.0649 ohms = 0.00255 ohms).
While the wire resistance changes about 4%, the total change is only 2.6 milliohms–which is a very minor change.
The generic formula for temperature affects on resistance is as follows:
Temperature Coefficient of Resistance Conclusion
After going through the above review the concept of temperature coefficient of resistance we can now establish a temperature coefficient of resistance definition. I hope you enjoy when reading this article, thank you.