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Wien, Wilhelm

radiation wavelength body formula

[veen] (1864–1928) German physicist: discovered the energy distribution formula for black body radiation.

Wien grew up in a farming family and originally planned to spend his life farming. He studied briefly at Göttingen and continued his degree work at Berlin from 1884. In 1886 Wien received his doctorate for research on light diffraction and associated absorption effects, and returned to manage his parents’ farm. A severe drought 4 years later forced the sale of the farm, and he became assistant to in Berlin. In 1900 he took up the professorship at Würzburg and after 20 years he was appointed as successor at Munich.

In 1892 Wien began research on thermal (or black body) radiation , a study which initiated the transition from classical physics to quantum theory. Wien showed that the wavelength ?, at which a black body radiation source at absolute temperature T emits maximum energy, obeys a law: ? T = constant = 0.29 cm K (the constant was measured by ). This is known as Wien’s displacement law; in accord with it a red-hot black body on further heating emits shorter-wavelength radiation and becomes white hot as the wavelength of maximum radiation shifts from the long wavelength (red) end to the centre of the visible spectrum.

Developing this, in 1896 he produced Wien’s formula describing the distribution of energy in a radiation spectrum as a function of wavelength and temperature. It was based on an assumption that a hot body consists of a large number of oscillators emitting radiation of all possible frequencies and all in thermal equilibrium. Interestingly, Wien’s formula is well obeyed at short wavelengths but is clearly wrong for longer values while produced a formula accurate at longer wavelengths but not at lower ones.

Planck gave much thought to these discrepancies and showed that, if one assumed that radiation could be emitted only in ‘packets’ of a minimum energy (which he called quanta), then a radiation law could be calculated that was obeyed accurately at all wavelengths. Planck published his quantum theory in 1900, aware that its assumptions had no justification in classical physics and yet, as they appeared correct, a major revolution in physical science was inevitable. Wien was awarded the Nobel Prize for physics in 1911.

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