Wilhelm Wien

Wilhelm Wien , 1864-1928, German physicist. He was professor at the universities of Giessen (1899), Würzburg (1900-1920), and Munich (from 1920). He received the 1911 Nobel Prize in Physics for his studies on the radiation of heat from black objects. He is noted also for his work on hydrodynamics, X rays, and the radiation of light.

Wien's displacement law The relation between the wavelength of peak emission from a black body and its temperature. At low temperatures black-body radiation is confined mainly to the infrared region of the spectrum, but at progressively higher temperatures the peak of the emission is displaced to progressively shorter wavelengths. According to the law, the wavelength of peak emission, λ_max, multiplied by T, the thermodynamic temperature of the body, is a constant. Although celestial bodies are not perfect black bodies, the displacement law is still useful for predicting the wavelengths near which most of their radiation is emitted. For example, the cosmic background radiation has T = 2.7 K and λ_max = 1 mm; a cool, red star has T = 3000 K and λ_max = 1 μm (in the infrared); the Sun, T = 6000 K and λ_max = 500 nm (visible); the hottest normal stars, T = 30 000 K and λ_max = 100 nm (ultraviolet); planetary nebula nuclei T = 100 000 K and λ_max = 30 nm (extreme ultraviolet). The law is named after the German physicist Wilhelm Wien (1864–1928).