Temperature Coefficient

 

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 t₁^oC and after raising the temperature, its resistance becomes R₂ at t₂^oC. 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 t₁^oC. 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 / Substances The temperature coefficient of resistance of some materials / substances at 20^oC 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 α_o is the temperature coefficient of resistance of material at 0^oC, then from equation (2), the resistance of material at t^oC, Where, R₀ is the Resistance of material at 0^o C Similarly, if the temperature coefficient of resistance of material at t^oC is αt, then the resistance of the material at 0^oC, from equation (2) Where, R_t is the Resistance of material at t^o C From equation (3) and (4) Where, α₁and α₂ the temperature coefficient of resistance of material at t₁^oC and t₂^oC 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.