Susceptiibiliteetti

Susceptiibiliteetti is a Finnish term for susceptibility, the propensity of a system to respond to external influences. The concept appears across sciences and is used to quantify how strongly an object or organism reacts to applied fields or stimuli, as well as to biological or ecological stressors.

In physics and materials science, magnetic susceptibility χm characterizes how a material becomes magnetized in an external magnetic field, while electric (dielectric) susceptibility χe describes how it polarizes in an electric field. In SI units, polarization P relates to E by P = ε0 χe E, and magnetization M relates to H by M = χm H. Susceptibility is often treated as a property of the material independent of field strength in the linear regime; χ is dimensionless for weak fields. Dynamic susceptibility describes frequency-dependent responses.

The fluctuation-dissipation theorem links susceptibility to fluctuations: χ is proportional to the variance of the corresponding order parameter, revealing a deep connection between response and intrinsic fluctuations.

In biology and health, susceptibility refers to the propensity of an individual or population to acquire a disease or condition when exposed to a causal agent. It depends on genetics, age, immunity, and environmental factors. Susceptibility can be modified by vaccination, nutrition, and prior exposure.

Measurement and applications: susceptibility is inferred from response to controlled stimuli, such as magnetometers, dielectric spectroscopy, or exposure studies in epidemiology. Understanding susceptibility informs material design, medical risk assessment, and ecological management.