Physics: 1918

Planck, Max Karl Ernst Ludwig pronounced plahngk, (1858-1947), was a German theoretical physicist who concentrated on the study of thermodynamics. He was concerned with the phenomena of absorption and emission of heat and other kinds of radiant energy. In 1900, Planck originated the quantum theory when he proposed his law of radiation. This new theory revolutionized the field of physics. In 1918, Planck was awarded the Nobel Prize for physics.

The major concept involved in Planck's theory was that an object that completely absorbs radiant energy, known to scientists as a black body, can only absorb or emit energy in tiny irreducible bits called quanta. The energy of each quantum is measured by multiplying the frequency of the radiant energy, v, by a universal constant, h. The constant is known as Planck's constant. Thus, energy (E) equals h times v. For example, a red flame emits less energy--that is, it is cooler--than a blue flame because red light has a lower frequency than blue light.

Planck's concept of energy quanta disagreed with former ideas about the nature of energy. Scientists had thought that energy flowed continuously. This view, however, could not explain the absorption and emission of energy by matter. Planck's theory accounted for this phenomenon.

In 1905, the German-born physicist Albert Einstein independently introduced the concept of light quanta. In 1913, Danish physicist Niels Bohr introduced quantum ideas into atomic theory and originated the modern theory of atomic structure.

Planck was born in Kiel, Germany. He studied at the universities of Munich and Berlin, and taught physics at the universities of Munich, Kiel, and Berlin.

Contributor: Roger H. Stuewer, Ph.D., Professor of the History of Science and Technology, University of Minnesota.

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