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Lenard, Phillipp Eduard Anton

light physics rays germany

[lay nah®t] (1862–1947) German physicist: investigated the photoelectric effect and cathode rays.

Lenard, the son of a wine-merchant, was educated at Budapest and in Germany, where he became professor at Kiel in 1898.

Before 1914 Lenard made a series of fundamental contributions to physics. He took the known fact that ultraviolet light falling on some metals causes electron emission (the photoelectric effect) and showed that this occurred only with light below a critical wavelength; that the electron velocity increases with falling wavelength and is independent of light intensity; and finally that increasing the light intensity produces a larger number of emitted electrons (1902) explained all these observations in 1905 and, with , introduced light quanta (photons) into physics, preparing the way for the development of quantum theory.

Lenard showed that cathode rays are an electron beam and received the 1905 Nobel Prize for physics for this work. The cathode rays would penetrate air and thin metal sheets and he deduced that atoms contained much empty space and both positive and negative charge (1903) work confirmed and extended this picture of the atom (1911).

Lenard had disputes over priority with (Lenard having narrowly failed to discover X-rays) and with , but his case does not appear strong. Lenard’s book Great Men of Science (1934) is marred by his omission of contemporaries with whom he had quarrelled. He was distressed that Germany lost the First World War, and afterwards by the death of his son and the loss of his savings by massive inflation. He developed an extreme dislike of the increasing mathematical sophistication of physics through the influence of Einstein and others. From 1919 Lenard argued for the establishment of ‘German physics’ untainted by Jewish theories, attacking Einstein as a socialist, pacifist and a Jew, but above all for being a theoretician. As the only leading scientist who was a Nazi supporter, Lenard acquired increasing power. In the 1930s a generation of disillusioned scientists left Germany, most of Germany’s capacity to achieve creative physical science departing with them.

Lennix, Harry J. (1965–) [next] [back] Lemmons, Kasi (1959–)

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