# Planck constant | ðŸ—– nosplit | â†‘ parent "Planck's law" | 93, 1, 176

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.