Wiedemann-Franz Law

Definition

The Wiedemann-Franz Law states that the ratio of the thermal conductivity (K) to the electrical conductivity (σ) of a metal is proportional to the temperature (T). This relationship implies that good electrical conductors are also good thermal conductors, establishing a connection between thermal and electrical properties of materials.

5 Must Know Facts For Your Next Test

1. The Wiedemann-Franz Law can be expressed mathematically as $$\frac{K}{\sigma} = L \cdot T$$, where L is the Lorenz number, a constant for a given metal.
2. This law is primarily applicable to metals and provides insight into their conductive properties, particularly at higher temperatures.
3. The Lorenz number (L) varies between different metals, with typical values around 2.44 x 10^-8 WΩ/K^2 for good conductors like copper.
4. In non-metals and semiconductors, the Wiedemann-Franz Law may not hold true due to differences in electron mobility and phonon interactions.
5. Understanding the Wiedemann-Franz Law helps in material selection for applications where both thermal and electrical conductivity are critical, such as in electronics and thermoelectric devices.

Review Questions

• How does the Wiedemann-Franz Law relate thermal conductivity to electrical conductivity in metals?
  • The Wiedemann-Franz Law shows that the ratio of thermal conductivity to electrical conductivity is proportional to temperature. This means that as temperature increases, both thermal and electrical conductivities will increase for metals, indicating a close relationship between these two properties. This law suggests that materials that are good at conducting electricity are also typically good at conducting heat.
• Discuss the implications of the Wiedemann-Franz Law in selecting materials for electronic components.
  • When selecting materials for electronic components, the Wiedemann-Franz Law helps predict how materials will perform under thermal and electrical stress. Since metals with high electrical conductivity also exhibit high thermal conductivity, they are often preferred in applications such as heat sinks and electrical connectors. Understanding this relationship can guide engineers in optimizing designs for performance and efficiency.
• Evaluate the limitations of the Wiedemann-Franz Law when applied to non-metals and semiconductors.
  • While the Wiedemann-Franz Law holds true for most metals, its applicability diminishes in non-metals and semiconductors due to distinct mechanisms governing thermal and electrical conduction. Non-metals often rely on phonon transport for thermal conduction, while semiconductors exhibit complex behaviors involving charge carriers. These differences can lead to situations where high electrical conductivity does not correlate with high thermal conductivity, complicating predictions based on the Wiedemann-Franz Law.

Related terms

Thermal Conductivity: The ability of a material to conduct heat, which is a crucial property in determining how heat moves through different materials.

Electrical Conductivity:

The measure of a material's ability to conduct an electric current, which is essential for understanding how well a material can transmit electricity.

Metals: A group of elements that are typically good conductors of both heat and electricity, exhibiting properties such as malleability, ductility, and luster.