Definition of Planck's constant
: a constant that gives the unvarying ratio of the energy of a quantum of radiation to its frequency and that has an approximate value of 6.626 × 10^{−34} J·s —symbol h
Origin and Etymology of planck's constant
Max K. E. L. Planck
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Biographical Note for planck's constant
Planck
\ˈpläŋk\,Max Karl Ernst Ludwig
(1858–1947), German physicist. Planck is credited with originating the quantum theory in physics. Throughout his career he taught theoretical physics at a succession of German universities. In 1900 he introduced Planck's constant as a part of his accurate formulation of the distribution of the radiation emitted by a blackbody, which is a perfect absorber of radiant energy. His discoveries established the field of quantum physics. Planck is also remembered for his work relating to thermodynamics and mechanics and to electrical and optical problems associated with radiation of heat and with the quantum theory. He was awarded the Nobel Prize for Physics in 1918.Learn More about planck's constant

Britannica.com: Encyclopedia article about Planck's constant
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