absorptívity

Absorptivity is a dimensionless quantity that describes how effectively a material absorbs electromagnetic radiation of a specific wavelength. It is defined as the ratio of the absorbed radiation to the incident radiation. Absorptivity is a value between 0 and 1, where 0 means no radiation is absorbed and 1 means all radiation is absorbed. This property is also known as the absorptive power.

The absorptivity of a material is not a constant but depends on the wavelength of the incident radiation. This wavelength-dependent absorptivity is often referred to as spectral absorptivity. Understanding spectral absorptivity is crucial in many fields, such as solar energy harvesting, where materials are designed to absorb specific wavelengths of sunlight, and in thermal imaging, where different materials absorb and emit infrared radiation differently.

In broader contexts, absorptivity can also refer to the capacity of a substance to absorb other substances, such as gases absorbed by liquids or solids, or liquids absorbed by solids. This absorption can be a surface phenomenon (adsorption) or a bulk phenomenon (absorption). In physics and engineering, however, the term most commonly refers to the absorption of electromagnetic radiation.

The complementary properties to absorptivity are reflectivity (reflectivity) and transmissivity (transmissivity). For opaque materials, reflectivity and absorptivity sum to 1, as no radiation is transmitted. For transparent or translucent materials, transmissivity also plays a role, and the sum of absorptivity, reflectivity, and transmissivity equals 1.