The electrical resistivity is a characteristic of a material. Its unit is the ohm meter. The resistivity indicates how strongly this material opposes to the flow of electric current.
The resistivity [ρ] (rho) is defined as:
ρ = R * A / L
where:
- ρ is the resistivity with ohm meter units
- R is the electrical resistance in ohms
- L is the length of the material measured in meters
- A is the crossed area measured in meters2
From the previous formula, we can find the value of a given sample if we know its length, the cross area and the material (the resistivity) it was made of.
R = ρ * L / A
- The greater the length or the smaller the cross-sectional area, the more the resistance.
- The smaller the length or greater the cross-sectional area, the less the resistance
Typical values of resistivity of various materials at 23° C are:
The resistivity depends on the temperature
The resistivity of a metal increases when the temperature goes up. The opposite case happens with semiconductors where its value decreases.
The inverse of the resistivity is called conductivity (σ) [sigma]
σ = 1 / ρ
