Thermal–Electrical Conductivity Link in Metals The empirical law stating that K / (σ * T) is approximately a universal constant for metals (where K is thermal conductivity, σ is electrical conductivity, and T is absolute temperature) is known as:

Introduction / Context:
In metals, the same electrons carry both heat and charge. This leads to a remarkable proportionality between thermal conductivity and electrical conductivity, once temperature is accounted for, summarized by K/(σT) ≈ constant. This principle is important for interpreting transport measurements and designing cryogenic or high-heat-flux components in electronics.

Given Data / Assumptions:

• Material is a simple metal with electron-dominated transport.
• Temperature not so low that impurity scattering dominates entirely.
• Classical/quantum free-electron picture applies approximately.

Concept / Approach:

The Wiedemann–Franz law states K/(σT) = L, where L is the Lorenz number (about 2.44 × 10^-8 W Ω K^-2). This emerges from free-electron theory and Fermi–Dirac statistics when energy and momentum relaxation share similar scattering mechanisms. Deviations occur in alloys, at very low temperatures, or where phonon contributions and inelastic scattering are significant.

Step-by-Step Solution:

Verification / Alternative check:

Experimental plots of K vs σ*T for many metals cluster near the same slope (L), validating the law over broad conditions.

Why Other Options Are Wrong:

• Lorentz law typically refers to force on charges in E and B fields; Curie–Weiss concerns magnetic susceptibility; “Kittel law” is not a named transport law here.

Common Pitfalls:

Confusing the Lorenz number with Lorentz force; overlooking temperature regimes where phonons dominate thermal transport.

Final Answer:

Wiedemann–Franz law