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 / o C (at 20 o C) 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% 0.0000
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