Proportionality factor in the Planck-Einstein relation between light energy and frequency.

And analogously for matter, appears in the de Broglie relations relating momentum and frequency.

A very direct way of thinking about it is to think about what would happen in a double-slit experiment.

Also appears in the Schrodinger equation, basically as a consequence/cause of the de Broglie relations most likely.

Defined exactly in the 2019 revision of the International System of Units.

- Planck's law | 104, 362, 3
- Black-body radiation experiment | 33, 395, 4
- Quantum mechanics experiments | 34, 1k, 14
- Quantum mechanics | 170, 11k, 165
- Particle physics | 140, 19k, 291
- Physics | 276, 25k, 429
- Natural science | 0, 30k, 686
- Science | 0, 36k, 821
- Ciro Santilli's Homepage | 238, 147k, 2k

- Kilogram | 37, 42, 1