Resistivity is usually symbolised with the greek letter 'rho' (ρ) and is measured in ohm metres.
What does the (electrical) resistance (R) of a sample substance depend on?
- The Type of Material
- The Cross-Sectional Area (a) of the sample
- The Length (l) of the sample
Resistance is proportional to length
Resistance is inversely proportional to cross-sectonal area
Combine these two and you get:
Resistance is proportional to length divided by cross-sectonal area.
Resistance = (ρl)/a
ρ = resistivity constant for the material
ie. The resistance of the sample equals the length divided by the cross-sectional area, all multiplied by the resistivity constant for the material.