Planck's constant

or Planck constant

noun Physics.

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. Symbol: h

Origin of Planck's constant

First recorded in 1905–10; named after M. K. E. Planck Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for planck constant

Planck constant

Planck's constant


a fundamental constant equal to the energy of any quantum of radiation divided by its frequency. It has a value of 6.62606876 × 10 –34 joule secondsSymbol: h See also Dirac constant
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

planck constant in Medicine

Planck's constant



The constant of proportionality relating the energy of a photon to the frequency of that photon. Its value is approximately 6.626 X 10-34 joule-second.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

planck constant in Science

Planck's constant


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 X 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. See also Dirac's constant quantize.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

planck constant in Culture

Planck's constant

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.


Knowing Planck's constant sets the scale of energy for events in which the atom and subatomic particles take part.
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.