Biography of Philipp Lenard
Nobel Physicist Famous for His Photoelectric Effect Investigation
Sep 2, 2008
Philipp Lenard (1862 - 1947) was a German-Hungarian physicist best known for his study of cathode rays and his investigation of the photoelectric effect. It had been known for some time that light falling on certain metals would cause the emission of electrons. Lenard meticulously investigated the effect but it was left to Albert Einstein to explain the significance of these results in 1905 by linking them to the new quantum theory of Max Planck.
Life and Education
Philipp Eduard Anton Lenard was born in Pozsony, Bratislava on July 7, 1862. His father was a wine merchant but Philipp preferred science over learning his father's business. He studied under the illustrious scientists Bunsen and Helmholtz, and obtained his doctoral degree in 1886 at the University of Heidelberg.
After posts at Aachen, Bonn, Breslau, Heidelberg (1896-1898), and Kiel (1898-1907), Lenard returned finally to the University of Heidelberg in 1907 as the head of the Philipp Lenard Institute, where he remained until his retirement in 1931.
Phosphorescence and Luminescence
Early work included studies of phosphorescence and luminescence. He showed that the maximum intensity of phosphorescent light is obtained when a certain definite proportion of impurities are present, and the intensity is diminished if this proportion is increased.
Meteorological Contributions
Lenard conducted studies on the size and shape distributions of raindrops in a novel wind tunnel in which water droplets of various sizes could be held stationary for a few seconds. He was the first person to study what has been termed the Lenard effect in 1892. This is the separation of electric charges accompanying the aerodynamic breakup of water drops. It is also known as spray electrification or the waterfall effect.
Photoelectric Investigation
Starting in 1899 Lenard investigated why the photoelectric effect could only be produced by ultraviolet or shortwave light. In the course of his experiments he established two anomalous results. He found that:
- The speed with which the electron was emitted was a function of the wavelength of the light used – the shorter the wavelength the faster the electron.
- Increasing the intensity of the light did not affect the speed but did, surprisingly, increase the number of electrons emitted.
Albert Einstein explained the significance of these results in 1905 by producing his quantitative law and developing the theory of quanta of light or photons, which was verified much later by Millikan.
Cathode Rays
Lenard also did important work on cathode rays (electrons) for which he received the Nobel Prize for physics in 1905. He demonstrated how electrons could be induced to leave the evacuated tube in which they were produced, penetrate thin metal sheets, and travel a short distance in the air, which would become conducting. On the basis of this work he proposed a model of the atom in which it is made from ‘dynamids’, units of positive and negative charge. This was, however, soon superseded by the nuclear atom of Ernest Rutherford.
Later Years and Legacy
Lenard retired from Heidelberg Univerisity as professor of theoretical physics in 1931. He achieved emeritus status there, but he was expelled from his post by Allied occupation forces in 1945 when he was 83. He died two years later in Messelhausen, Germany.
Lenard is sometimes remembered as a strong German nationalist who despised English physics, which he considered as having stolen their ideas from Germany. During the Nazi regime, he was an outspoken proponent of the idea that Germany should rely only on "Deutsche Physik" (German physics) and in his opinion, ignore the fallacious and perhaps deliberately misleading ideas of "Jewish physics", by which he meant the theories of Albert Einstein.
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