Philipp Lenard
1862–1947, Pressburg, Austria-Hungary (now Bratislava, Slovakia), Messelhausen, Germany
German physicist who measured the laws of the photoelectric effect and studied cathode rays, winning the 1905 Nobel Prize in Physics.
Born in Pressburg, Austria-Hungary (now Bratislava), Lenard was an assistant to Heinrich Hertz before holding chairs at Breslau, Aachen, Heidelberg, and Kiel. A superb experimenter on cathode rays and the photoelectric effect, he became in his later years a champion of the xenophobic 'German physics' movement during the Nazi era and an outspoken critic of Einstein's relativity.
Nobel-winning work
The 1905 Nobel Prize was awarded 'for his work on cathode rays'. From 1894, Lenard devised the 'Lenard window' — a thin aluminium foil sealed into a cathode tube — which let cathode rays pass outside the vacuum so their penetrating power in air could be measured. He showed they were absorbed in a density-dependent manner and were deflected by magnetic fields like negatively charged particles — important evidence in the debates about the nature of cathode rays.
Lenard also established the measured laws of the photoelectric effect: in 1902 he showed that the energy of electrons emitted by ultraviolet light depended on the light's frequency but not on its intensity — a result inexplicable by classical wave theory, and resolved only by Einstein's photon hypothesis of 1905. This precision measurement was a decisive step on the road to the quantum theory of light.
Workplaces: University of Heidelberg, University of Kiel
Germany