Planck's constant

American  

Or Planck constant

noun

Physics.

1. the fundamental constant of quantum mechanics, expressing the ratio of the energy of one quantum of radiation to the frequency of the radiation and approximately equal to 6.624 × 10− 27 erg-seconds. h

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Planck's constant Scientific  

/ plängks /

1. A physical constant that is used extensively in quantum mechanics and fixes the scale of quantization of many phenomena, such as the relation between the energy of a photon (a quantum of light) and its wavelength. Its value is approximately 6.626 × 10 ^{- 34} joule-seconds (equivalent to units of angular momentum). Planck's constant is fundamental to phenomena as the quantization of angular momentum and is used in Heisenberg's Uncertainty Principle.

2. See also Dirac's constant quantize

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Planck's constant Cultural  

1. A universal constant, first discovered by Max Planck, that states the mathematical relationship between the frequency of an electromagnetic wave and the energy in that wave. Planck's discovery unifies the seemingly contradictory observations that energy sometimes acts like a wave and at other times acts as if it is made up of particles.

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Discover More

Knowing Planck's constant sets the scale of energy for events in which the atom and subatomic particles take part.

Etymology

Origin of Planck's constant

First recorded in 1905–10; named after M. K. E. Planck

Example Sentences

However, since then, it has been defined by what is known as Planck's constant, which relates to the quantum nature of energy.

From Barron's • Oct. 15, 2025

If the world were 'classical' -- that is, if Planck's constant were exactly zero -- this attractive force would be impossible to overcome.

From Science Daily • Apr. 26, 2024

She knew Planck’s constant, which was the key to defeating the giant blood monster.

From The Guardian • Dec. 20, 2019

The four will be based on Planck's constant, the elementary charge, the Boltzmann constant and the Avogadro constant, respectively.

From Scientific American • Oct. 29, 2018

Once it was "July," then "soup kettle" and "Planck's constant."

From The Electronic Mind Reader by Blaine, John