läpäisykerroin

Läpäisykerroin, in English often called the transmission coefficient, is a dimensionless quantity that describes how easily a barrier or interface allows a certain phenomenon to pass through. It represents the fraction or probability that the incident quantity, such as light, heat, a chemical species, or particles, is transmitted rather than reflected or absorbed. The exact meaning and calculation depend on the context and the quantity considered.

In optics and radiative transfer, the läpäisykerroin refers to the fraction of incident electromagnetic radiation that passes through a material or layer. Transmission depends on material properties like refractive index and absorption coefficients, as well as the angle of incidence. The transmitted intensity I is often expressed as I = T I0, where T is the transmission coefficient (0 ≤ T ≤ 1).

In membrane science and diffusion theory, the term describes how readily a substance permeates a barrier. Here the transmission coefficient is related to the flux of solute across a membrane relative to the driving force, such as a concentration difference. Permeability concepts in this area combine diffusion and partitioning effects and are used to quantify barrier performance in filtration, packaging, and drug delivery.

In quantum mechanics, a similar coefficient—the transmission probability—gives the likelihood that a particle will tunnel through or pass a potential barrier. It plays a central role in tunneling phenomena and barrier scattering.

Measurement and interpretation of läpäisykerroin require specifying the context, quantities involved, and often the geometry of the barrier. Reported values are context-specific and may involve different units or normalization conventions. See also transmittance, permeability, and diffusion.