In 1896 Wien empirically determined a distribution law ofblackbody radiation,[2] later named after him:Wien's 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 calledPlanck's law, which led to the development ofquantum theory. However, Wien's other empirical formulation, calledWien's displacement law, is still very useful, as it relates the peak wavelength emitted by a body (λmax), to the temperature of the body (T). In 1900 (following the work ofGeorge Frederick Charles Searle), he assumed that the entire mass of matter is of electromagnetic origin and proposed the formula for the relation between electromagnetic mass and electromagnetic energy.
Wien developed theWien filter (also known as velocity selector) in 1898 for the study of anode rays. It is a device consisting of perpendicular electric and magnetic fields that can be used as a velocity filter for charged particles, for example in electron microscopes and spectrometers. It is used in accelerator mass spectrometry to select particles based on their speed. The device is composed of orthogonal electric and magnetic fields, such that particles with the correct speed will be unaffected while other particles will be deflected. It can be configured as a charged particle energy analyzer, monochromator, or mass spectrometer.
While studying streams ofionized gas, Wien, in 1898, identified a positive particle equal in mass to thehydrogenatom. Wien, with this work, laid the foundation ofmass spectrometry.J. J. Thomson refined Wien's apparatus and conducted further experiments in 1913 then, after work byErnest Rutherford in 1919, Wien's particle was accepted and named theproton.
