Philipp Eduard Anton von Lenard
Lenard, Philipp Eduard Anton von (1862-1947), a German physicist, won the Nobel Prize in physics in 1905 for his studies of the properties of the streams of electrons called cathode rays.
Lenard was born June 7, 1862, in Pressburg, Austria-Hungary (now Bratislava, Slovakia), the only child of Philipp von Lenard, a wine merchant, and the former Antonie Baumann. After his mother died, Lenard's aunt raised him and married his father. At a young age, Lenard read college textbooks and performed chemistry and physics experiments on his own. He earned his doctorate in physics from the University of Heidelberg in 1886.
At Heidelberg, Lenard researched how light is given off by the process of phosphorescence and luminescence. He discovered that some materials glow in the dark, after exposure to light, only if they contain traces of certain heavy metals such as copper and bismuth.
Working with German physicist Heinrich Rudolf Hertz at University of Bonn, Lenard investigated cathode rays, which travel from the negative electrode (cathode) of a glass vacuum tube to the opposite end.
In 1892, Lenard constructed a cathode-ray tube with a thin sheet of aluminum serving as a window to keep the vacuum contained but to let cathode rays out. With this “Lenard window,” as it came to be called, he showed that the rays decreased in number as the distance from the tube increased. He also showed that the density of materials affected their ability to absorb cathode rays. He also demonstrated how light striking a metal surface could create a cathode ray. This became known as the photoelectric effect.
Lenard's discoveries conflicted with the theories of his day. However, his experimental data were clarified by German physicist Albert Einstein, who explained the photoelectric effect in 1905 by showing that light consists of particles of energy called quanta, later called photons.
As he continued his research on phosphorescence, cathode rays, and other physics problems, he taught at the universities of Breslau, Aachen, Heidelberg, and Kiel.