MARGRETHE BOHR COLLECTION / AMERICAN INSTITUTE OF PHYSICS / SCIENCE PHOTO LIBRARY MARGRETHE BOHR COLLECTION / AMERICAN INSTITUTE OF PHYSICS / SCIENCE PHOTO LIBRARY
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Niels Bohr and Max Planck. Historical portrait of the Danish physicist Niels Henrik David Bohr (1885-1962) with the German physicist Max Planck (1858-1947). Planck is at right. They were central figures in the development of quantum theory. Planck proposed in 1900 that radiation is emitted in discrete packets (quanta). Bohr's 1913 model of the hydrogen atom used quantized energy levels for electrons orbiting the nucleus. Bohr received the Nobel Prize for Physics in 1922, as Planck had in 1918. Photographed in 1930.
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