The Wiedemann-Franz law states that the ratio of thermal conductivity to electrical conductivity for a material is approximately constant, independent of the material for a fixed temperature. Moreover, as temperature changes, the ratio of thermal conductivity to electrical conductivity for a material is directly proportional to the temperature of the material. Which of the following is true of the Wiedemann-Franz law?
(i) The Wiedemann-Franz law applies only to ceramics and plastics.
(ii) The Wiedemann-Franz law applies best to elemental metals.
(iii) The Wiedemann-Franz law is based on the free electron theory of metals, in which both thermal energy andelectrical charge are transported primarily by free electrons.
(iv) The Wiedemann-Franz law is based on the Pauling’s rules for electronegativity, in which the electrical conductivity and thermal conductivity of ceramic and plastic materials are related to the percentage of ionicity of the atomic bonds in the structure.