Planck's constant

or Planck constant

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

Planck's constant

/ 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

Planck's constant

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.

Notes

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

Word History and Origins

Origin of Planck's constant¹

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

Example Sentences

These quantum phenomena depend on Planck's constant, the fundamental constant of nature that determines how the quantum world differs from our large-scale world, but in a simple way.

From Science Daily

Despite the ridiculous smallness of this constant -- expressed in everyday units of kilograms, metres and seconds it takes a value that starts at the 34th decimal place after the comma -- the fact that Planck's constant is not exactly zero is enough to compute such quantum effects.

From Science Daily

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

In thin layers and at large enough magnetic fields, this resistance begins to develop discreet steps with values of exactly h/ne2, where h is the Planck's constant, e is the elementary charge, and n is an integer number.

From Science Daily

The ability to precisely measure resistance comes from von Klitzing’s discovery that resistance is quantized at values that are proportional to a combination of two fundamental physical constants: the charge of the electron and Planck’s constant.

From Nature