Editing Action (physics) (section)

=== Planck's quantum of action ===
The [[Planck constant]], written as <math>h</math> is the quantum of action.<ref>{{Cite web |title=Max Planck Nobel Lecture |url=https://www.nobelprize.org/prizes/physics/1918/planck/lecture/ |url-status=live |archive-url=https://web.archive.org/web/20230714164215/https://www.nobelprize.org/prizes/physics/1918/planck/lecture/ |archive-date=2023-07-14 |access-date=2023-07-14}}</ref> The quantum of [[angular momentum]] is <math>\hbar = \frac{h}{2\pi}</math>. These constants have units of energy times time. They appear in all significant quantum equations, like the [[uncertainty principle]] and the [[de Broglie wavelength]]. Whenever the value of the action approaches the Planck constant, quantum effects are significant.<ref name=FeynmanII/>