Wiedemann–Franz law in metals In metals, the thermal conductivity K and electrical conductivity σ satisfy K/(σ T) = L. The constant L is called the:

Introduction / Context:The Wiedemann–Franz law connects heat and charge transport in metals via free electrons. It states that the ratio of thermal conductivity K to electrical conductivity σ, scaled by absolute temperature T, is approximately constant for many pure metals at moderate temperatures.

Given Data / Assumptions:

• Metallic conductor dominated by electron transport.
• Temperature range where classical free-electron model is a reasonable approximation.
• Phonon contributions to K not dominant.

Concept / Approach:The empirical relation is K / (σ T) = L. The proportionality constant L is known as the Lorenz number (not “Lattice constant”). For free electrons, Sommerfeld theory gives L ≈ 2.44 × 10^−8 W Ω K^−2 at room temperature, providing a useful cross-check between thermal and electrical measurements.

Step-by-Step Solution:Identify the law: Wiedemann–Franz.Recall the ratio form and the constant’s name.Select “Lorenz number” as the correct terminology.

Verification / Alternative check:Handbooks tabulate L values near 2.44 × 10^−8 W Ω K^−2 for many metals, with deviations at low temperatures due to impurity scattering and at high temperatures due to phonon effects.

Why Other Options Are Wrong:“Lattice constant” is a crystallographic spacing; “Langevin function” arises in paramagnetism; “Larmor” relates to precession frequency—none refer to K/(σ T).

Common Pitfalls:Confusing “Lorentz” with “Lorenz”—the correct name here is Lorenz number.

Final Answer:Lorenz number