Electrical conductivity

Definition

Electrical conductivity is a measure of a material's ability to conduct electric current, defined as the ratio of current density to the electric field strength. This property is influenced by the availability of charge carriers, such as free electrons in metals, and is fundamental in understanding how materials behave under electric fields. Conductivity is crucial for distinguishing between conductors, insulators, and semiconductors, and relates directly to concepts like band theory and the free electron model.

5 Must Know Facts For Your Next Test

1. Conductivity varies significantly among different materials; metals typically have high electrical conductivity due to a large number of free electrons.
2. In semiconductors, electrical conductivity can be altered by doping, which introduces additional charge carriers.
3. The temperature of a material can influence its electrical conductivity; for most metals, conductivity decreases with increasing temperature due to increased atomic vibrations.
4. Superconductors exhibit zero electrical resistance below a certain critical temperature, allowing them to conduct electricity without energy loss.
5. The relationship between electrical conductivity and the free electron model helps explain why metals are good conductors, as free electrons can move easily through the lattice structure.

Review Questions

• How does the free electron model explain the high electrical conductivity observed in metals?
  • The free electron model describes metals as having a lattice of positively charged ions surrounded by a sea of delocalized electrons. These free electrons can move easily throughout the metal when an electric field is applied, allowing for efficient conduction of electric current. The presence of these mobile charge carriers is what gives metals their characteristic high electrical conductivity compared to other materials.
• Discuss the role of band theory in understanding the electrical conductivity of semiconductors versus insulators.
  • Band theory categorizes materials based on their energy bands, specifically the conduction band and valence band. In semiconductors, the band gap between these two bands is small enough that thermal energy can promote electrons from the valence band to the conduction band, enhancing conductivity. In contrast, insulators have a larger band gap, making it difficult for electrons to jump to the conduction band under normal conditions, resulting in very low conductivity.
• Evaluate how temperature affects electrical conductivity in different materials and explain the underlying mechanisms.
  • Temperature has a varying impact on electrical conductivity depending on the type of material. In metals, increased temperature leads to more atomic vibrations that scatter free electrons, causing a decrease in conductivity. Conversely, in semiconductors, higher temperatures can provide enough energy for more electrons to cross the band gap into the conduction band, resulting in increased conductivity. This difference highlights how charge carrier availability and mobility interact with thermal energy to influence overall conductivity.

Related terms

Resistivity:

The inherent property of a material that quantifies how strongly it opposes the flow of electric current, which is inversely related to conductivity.

Semiconductors:

Materials that have electrical conductivity between conductors and insulators; their conductivity can be modified by temperature or impurities.

Band Gap: The energy difference between the valence band and the conduction band in a solid, affecting its electrical conductivity; smaller band gaps typically lead to higher conductivity.