WILHELM WIEN

WILHELM WIENPrepared by:Jannat manchanda

Early years

Wilhelm Carl Werner Otto Fritz Franz Wien was a german physicst born on January 13, 1864 at Fischhausen, in East Prussia. He was the son of the landowner Carl Wien, and seemed destined for the life of a gentleman farmer, but an economic crisis and his own secret sense of vocation led him to University studies.EDUCATIONIn 1879, Wien went to school in Rastenburg and from 1880-1882 he attended the city school ofHeidelberg. In 1882 he attended theUniversity Of Gottingenand the University of Berlin. From 1883-85, he worked in the laboratory ofHermann von Helmholtzand, in 1886, he received hisPh.D.with a thesis on the diffraction of light upon metals and on the influence of various materials upon thecolourof refracted light. From 1896 to 1899, Wien lectured atRWTH Aachen University. In 1900 he went to theUniversity Of Wurzburgand became successor ofWilhelm Conrad Rontgen.CAREERIn 1896 Wien empirically determined a distribution law ofblackbody radiation, later named after him:Wiens Law.Max Planck, who was a colleague of Wien's, did not believe in empirical laws, so using electromagnetism and thermodynamics, he proposed a theoretical basis for Wien's law, which became theWien-Planck Law. However, Wien's law was only valid at high frequencies, and underestimated the radiancy at low frequencies. Planck corrected the theory and proposed what is now calledPlancks Law, which led to the development ofQuantum Theory.Wien's other empirical formulation maxT=constant, calledWiens Displacement Law, is still very useful, as it relates the peak wavelength emitted by a body (max), to the temperature of the body (T)While studying streams ofIonized gas, Wien, in 1898, identified a positive particle equal in mass to theHydrogen atom. Wien, with this work, laid the foundation ofmass spectrometry. J.J. Thomsonrefined Wien's apparatus and conducted further experiments in 1913 then, after work byErnest Rutherfordin 1919, Wien's particle was accepted and named theproton. During April 1913, Wien was a lecturer atColumbia University.

Wiens displacement lawWien's displacement lawstates that thewavelengthdistribution ofthermal radiationfrom ablack bodyat any temperature has essentially the same shape as the distribution at any other temperature, except that each wavelength is displaced on the graph. Apart from an overallT3multiplicative factor, the average thermal energyin each mode with frequency only depends on the ratio /T. Restated in terms of the wavelength =c/, the distributions at corresponding wavelengths are related, where corresponding wavelengths are at locations proportional to 1/T.Blackbody Radiationapproximates to Wien's law at high frequency.

There is an inverse relationship between the wavelength of the peak of the emission of a black body and itstemperature when expressed as a function of wavelength, and this less powerful consequence is often also called Wien's displacement .maxT=constantwhere maxis the peak wavelength,Tis the absolute temperature of the black body, andbis aconstant of proportionalitycalledWien's displacement constant, equal to2.8977685(51)103mK

examplesLight from the Sun: The effective temperature of the Sun is 5778 K. Peak emission at a wavelength of 2.90 million nm K/ 5778 K = 502 nm i.e. wavelength of green light, and it is near the peak sensitivity of the human eye.The claim is then made that the human eye evolved to be most sensitive to the peak emission from the Sun. In fact, Wien's law says that the Sun's peak emissionper unit wavelengthis at 502 nm. When the spectrum is reckoned per frequency interval, the Sun's peak emission appears at a frequency of 3.43 x 1014Hz; this means that the peak emissionper unit frequencyis at 3.43 x 1014Hz, which corresponds to a wavelength of 883 nm and is well into the infrared. That is, the apparent "peak" of the spectrum is significantly affected by the bookkeeping convention by which one describes the spectrum. (Evolution of the eye was more likely influenced by the spectral absorption properties of water than by the Sun's spectrum.)Light from incandescent bulbs and fires: Alightbulbhas a glowing wire with a somewhat lower temperature, resulting in yellow light, and something that is "red hot" is again a little less hot. It is easy to calculate that a wood fire at 1500 K puts out peak radiation at 3 million nm K /1500 K = 2000nm = 20,000. This is far more energy in the infrared than in the visible band, which ends about 7500 .Radiation from mammals and the living human body: Mammals at roughly 300 K emit peak radiation at 3 thousand m K / 300 K = 10 m, in the far infrared. This is therefore the range of infrared wavelengths thatpit vipersnakes and passive IR cameras must sense.

AchievementsHe won the 1911 Nobel Prize in physics for his discoveries regarding the laws governing the radiation of heat. Wien also studied cathode rays and X rays.In 1892 received thevenia legandiat the University of Berlin with a work on the localization of energy.