Resistivity and Conductivity

When cross-section area and physical composition of material are consistent (uniform), which is an ideal case, the resistivity of a material is an intrinsic property of a material.  Many conductors and resistors are manufactured with uniform materials and cross-sections making a useful application of the concept of resistivity.  This relationship between resistivity and resistance is described in Pouilet's Law for Resistivity in the following formula:

ρ = R • A/L

where:

• ρ = resistivity
• R = electrical resistance
• A = cross-section area
• L = length

Pouillet's Law is named after physicist Claud Pouillet (pictured) who was born on 16 Feb 1790 and died on 14 Jun 1868.  Pouillet was a member of the French Academy of Sciences. 

This calculator has Pouillet's Law in four forms:

• Pouillet's Resistivity: ρ = R • A/L 
• Pouillet's Resistance: R = (ρ • L)/A 
• Pouillet's Cross-section Area:  A = (ρ • L)/R 
• Pouillet's Length: L = (R • A ) / ρ