Resistivity: Intrinsic Resistance

RESISTIVITY: Intrinsic Resistance

If you increase the length of a wire or make its cross-sectional area smaller, the wire's resistance will increase. There is an intrinsic measure (the resistivity) of a material's resistance which does not depend upon either the length or the cross-sectional area but only upon the material's atomic structure.

R = Resistance (SI: Ω)
ρ = Electrical Resistivity (SI: Ω ^.m)
L = Length of the Wire (SI: m)
A = Cross-sectional Area of the Wire (SI: m ²)

One over the resistivity (s = 1/ρ) is a measure of the conductivity of a material. The larger the value of a material's s the larger will be the current flowing in the material for the same applied voltage.

Resistivity of Some Materials at 20 ^oC

Material Resistivity ρ
(Ω ^.m) Material Resistivity ρ
(Ω ^.m)

Conductors Semiconductors

Aluminum............. 2.82x10^-8 Carbon (graphite) 1.5x10^-5

Copper 1.72x10^-8 Germanium (pure) 4.6x10^-1

Gold 2.24x10^-8 Silicon (pure) 2.5x10²

Iron 9.71x10^-8 Insulators

Platinum 10.6 x10 ^-8

Silver 1.59x10^-8 Glass 10¹⁰ - 10 ¹⁴

Tungsten 5.65x10^-8 Rubber 10¹³ - 10 ¹⁶

Nickel 7.80x10^-8 Wood 10¹⁰

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