What is electrical conductivity and how is it defined?
Electrical conductivity is a fundamental physical quantity that describes how well a material can conduct electric current. It is represented by the symbol σ (sigma) or κ (kappa). The electrical conductivity of a material is the reciprocal of the electrical resistance and indicates how easily electrons or ions can move through a material.
GOBA supplies insulation materials with defined low electrical conductivity for electrical engineering applications.
How is electrical conductivity specified as a physical quantity?
The unit of electrical conductivity is Siemens per metre (S/m). In practice, mS/cm or μS/cm are also used for the conductivity of liquids. Metals such as copper (Cu) and silver (Ag) have very high conductivity, whereas insulators such as rubber or glass have very low conductivity. Semiconductors such as silicon (Si) can have their conductivity selectively altered by doping.
What role do electrons and ions play in electrical conductivity?
Electrical conductivity is based on the movement of charge carriers. In metals, free electrons perform this function, whereas in ionic solutions or semiconductors charged ions are responsible for the current flow.
- In metals, many freely moving electrons in the conduction band transport current.
- In semiconductors, conductivity depends on the number of free electrons and holes.
- In liquids, conduction occurs through ions in water or other dissolved electrically charged particles.
The mobility of electrons and ions directly influences the electrical conductivity of a substance or mixture.
What is the difference between conductance and specific conductivity?
Conductance (G) indicates how well an electrical conductor allows current to flow and is expressed in Siemens (S). Specific conductivity, by contrast, is material-dependent and describes the ability of a particular substance to conduct electric current, independent of its geometry.
How is electrical conductivity measured?
Electrical conductivity is measured using various methods:
- Direct measurement with two electrodes: A voltage is applied and the current flow is measured.
- Four-wire measurement method: Used for low resistances to avoid measurement errors from cable connections.
- Inductive measurement: Often used in liquids.
How is the measurement of conductivity related to electrical resistance?
Since conductivity is the reciprocal of electrical resistance, a material with low resistance has high conductivity, such as copper or silver.
Which factors influence the electrical conductivity of different substances?
How does temperature affect the conductivity of metals?
As temperature increases, the lattice vibration of the atoms rises, reducing the electron mobility. This means:
- Metals conduct better at low temperatures.
- Semiconductors become more conductive with rising temperatures.
This temperature dependence is important for electric light bulbs, where the resistance of the wire rises as it heats up.
What role does doping play in semiconductors?
Semiconductors such as silicon can have their conductivity selectively altered by doping with foreign atoms.
- N-doped semiconductors contain more free electrons.
- P-doped semiconductors have more holes, which enable electron flow.
Why is electrical conductivity relevant as a tensor?
In crystals, electrical conductivity can be anisotropic, meaning it differs in different directions. In such cases conductivity is treated as a second-order tensor. A band model illustrates electrical conductivity in crystals.
What practical applications does electrical conductivity have?
How is conductivity used in electrical engineering?
- Copper wires in power lines due to their high conductivity.
- Semiconductor components in computers and smartphones.
What role does conductivity play in geothermics?
The electrical conductivity of rock and water helps to analyse underground structures in geothermics.
How is electrical conductivity used in materials science?
- Temperature measurement with a current-carrying diode.
- Investigation of doping effects in semiconductors.
How does conductivity differ between metals, semiconductors and insulators?
What makes metals good electrical conductors?
Metals such as copper, silver and gold have many free electrons. The mean time of flight of the electrons between two collisions is high, which ensures low electrical resistance.
How can the conductivity of semiconductors be influenced?
Through doping and light irradiation, the electrical conductivity of semiconductors can be selectively increased or decreased.
Why do insulators have very low electrical conductivity?
Insulators such as glass or ceramics have no free electrons and are therefore electrically non-conductive. The electron binding is strong, so no electric current can flow.
GOBA Takeaway
Electrical conductivity is a fundamental physical property that describes how well a material conducts electric current. It depends on electrons, temperature, material structure and external influences. Metals are excellent conductors with high electron mobility. Semiconductors can change their conductivity through doping and temperature. Insulators block the flow of current almost entirely. The measurement and optimization of electrical conductivity is of decisive importance in electrical engineering, geothermics and materials science.