By Alan Osborne – Updated March 24, 2022
Resistivity and conductivity are fundamental electrical properties that determine how well a material permits the flow of electric current. While both terms are often used interchangeably, they describe opposite aspects of a conductor’s behavior.
Resistivity (ρ) measures the opposition a material presents to electric current per unit length and cross‑section. It is expressed in ohm‑metres (Ω·m). A high resistivity means the material resists current flow, converting more electrical energy into heat. For instance, the resistivity of copper at 20 °C is approximately 1.68 × 10⁻⁸ Ω·m, making it an excellent conductor.
Conductivity (σ) is the inverse of resistivity and quantifies how readily a material allows electric current to pass through it. It is measured in siemens per metre (S m⁻¹). Good conductors such as copper have σ ≈ 5.96 × 10⁷ S m⁻¹, whereas insulating materials like rubber have values many orders of magnitude lower.
Because σ = 1/ρ, the two properties are reciprocals: as conductivity increases, resistivity decreases, and vice versa. Consequently, a substance cannot simultaneously exhibit high conductivity and high resistivity.
Understanding resistivity and conductivity guides material selection in engineering:
In summary, resistivity and conductivity provide complementary insights into a material’s electrical behavior, enabling informed design choices across technology, industry, and research.
