Wiedemann–Franz law
In physics, the Wiedemann–Franz law states that the ratio of the electronic contribution of the thermal conductivity (κ) to the electrical conductivity (σ) of a metal is proportional to the temperature (T). κ σ = L T {\displaystyle {\frac {\kappa }{\sigma }}=LT} Theoretically, the proportionality constant L, known as the Lorenz number, is equal to L = κ σ T = π 2 3 ( k B e ) 2 = 2.44 × 10 − 8 V 2 ⋅ K − 2 , {\displaystyle L={\frac {\kappa }{\sigma T}}={\frac {\pi ^{2}}{3}}\left({\frac {k_{\rm {B}}}{e}}\right)^{2}=2.44\times 10^{-8}\;\mathrm {V^{2}{\cdot }K} ^{-2},} where kB is the Boltzmann constant and e is the elementary charge.