ONLINE ELECTRICAL ENGINEERING STUDY SITE

Temperature Coefficient of Resistance

The electrical resistance of conductors such as silver, copper, gold, aluminum etc., depends upon collusion process of electrons with in material. As the temperature increase, this electron collusion process becomes faster, which results in increased resistance with rise in temperature of 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) If at a particular temperature, we know the resistance and temperature coefficient of resistance of material, we can find out the resistance of material at other temperatures by using equation (2).

The Temperature Coefficient of Resistance of some Materials or Substances The temperature coefficient of resistance of some materials / substances at 20oC are listed below-

Sl. No.Material / SubstancesChemical Symbol / Chemical compositionTemperature coefficient of resistance /oC (at 20oC)
1SilverAg0.0038
2CopperCu0.00386
3GoldAu 0.0034
4AluminumAl 0.00429
5TungstenW0.0045
6IronFe0.00651
7PlatinumPt0.003927
8ManganinCu = 84% + Mn = 12% + Ni = 4%0.000002
9Mercury Hg0.0009
10NichromeNi = 60% + Cr = 15% + Fe = 25%0.0004
11ConstantanCu = 55% + Ni = 45%0.00003
12Carbon C- 0.0005
13Germanium Ge- 0.05
14SiliconSi- 0.07
15BrassCu = 50 - 65% + Zn = 50 - 35%0.0015
16NickelNi0.00641
17TinSn0.0042
18ZincZn0.0037
19ManganeseMn0.00001
20TantalumTa0.0033

Effect of Temperature on Temperature Coefficient of Resistance of a Material The temperature coefficient of resistance of a material is also changes with temperature. If αo is the temperature coefficient of resistance of material at 0oC, then from equation (2), the resistance of material at toC, Where, R0 is the Resistance of material at 0o C Similarly, if the temperature coefficient of resistance of material at toC is αt, then the resistance of the material at 0oC, from equation (2) Where, R_t is the Resistance of material at to C From equation (3) and (4) Where, α1and α2 the temperature coefficient of resistance of material at t1oC and t2oC respectively. Hence, if we know the temperature coefficient of resistance of a material at a particular temperature, we may find out the temperature coefficient of material at any other temperature by using equation (6). The conducting material are having large and positive temperature coefficient of resistance. Therefore, the resistance of conducting material (metals) rise with rise of temperature.

The semiconductors and insulating material are having negative temperature coefficient of resistance. Therefore, the resistance of semiconductors and insulators decrease with rise in temperature. Alloys, such as manganin, constantan etc. are having very low and positive temperature coefficient of resistance. Therefore, the resistance of alloys increase with rise in temperature but this rise in resistance is very low (almost negligible) as compare to metals, which makes these alloys suitable for using in measuring instruments.

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