Johtoisuus

Johtoisuus, often translated as conductivity, is a fundamental property of materials that describes their ability to conduct electric current. It is the inverse of resistivity, meaning a material with high electrical conductivity will have low electrical resistivity, and vice versa. The SI unit for electrical conductivity is siemens per meter (S/m).

In metals, electrical conductivity arises from the movement of free electrons. These electrons are not bound to individual atoms and can easily move through the material's crystal lattice when an electric field is applied. The efficiency of this movement is influenced by factors such as temperature, impurities, and the material's atomic structure. Higher temperatures generally lead to decreased conductivity in metals due to increased atomic vibrations hindering electron flow.

Semiconductors exhibit conductivity between that of conductors and insulators. Their conductivity can be significantly altered by doping, the intentional introduction of impurities, which increases the number of charge carriers (electrons or holes). This controlled conductivity makes semiconductors essential components in electronic devices.

Insulators, such as rubber or glass, have very low electrical conductivity because their electrons are tightly bound to atoms and are not free to move. Therefore, they resist the flow of electric current.

The concept of thermal conductivity is also related, describing a material's ability to conduct heat. While electrical conductivity deals with the movement of charge, thermal conductivity deals with the transfer of thermal energy, primarily through lattice vibrations (phonons) and the movement of free electrons in some materials.