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 / Substances Chemical Symbol / Chemical composition Temperature coefficient of resistance /oC (at 20oC) 1 Silver Ag 0.0038 2 Copper Cu 0.00386 3 Gold Au 0.0034 4 Aluminum Al 0.00429 5 Tungsten W 0.0045 6 Iron Fe 0.00651 7 Platinum Pt 0.003927 8 Manganin Cu = 84% + Mn = 12% + Ni = 4% 0.000002 9 Mercury Hg 0.0009 10 Nichrome Ni = 60% + Cr = 15% + Fe = 25% 0.0004 11 Constantan Cu = 55% + Ni = 45% 0.00003 12 Carbon C - 0.0005 13 Germanium Ge - 0.05 14 Silicon Si - 0.07 15 Brass Cu = 50 - 65% + Zn = 50 - 35% 0.0015 16 Nickel Ni 0.00641 17 Tin Sn 0.0042 18 Zinc Zn 0.0037 19 Manganese Mn 0.00001 20 Tantalum Ta 0.0033

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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