Resistivity and temperature coefficient of resistance

Resistivity:

Resistivity of any material is defined as amount of resistance shown by that material between two opposite faces of a unit cube of that material.

       1)R ∝ L (resistance is proportional to length)
       2)R ∝ 1 / A (resistance is inversely proportional to cross section area)
       Combining both proportionalities gives:

R ∝ L / A

R = ρ (L / A)

ρ = R (A / L)

Unit of the resistivity is ohm-meter 

Temperature coefficient of resistance:

Temperature coefficient of resistance of any material is the value  that measure of change in electrical resistance of any substance per  degree change of temperature.

     

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