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Concept

Planck constant

The image features a blurred, golden-yellow background with a central dark letter 'h' representing the Planck constant, a fundamental quantum of action introduced by Max Planck in 1900.

The fundamental quantum of action, denoted h, relating the energy of a photon to its frequency. Introduced by Max Planck in 1900 to explain blackbody radiation. Since 20 May 2019 it has been defined to have the exact value 6.62607015 × 10⁻³⁴ joule-seconds, with the kilogram, ampere, kelvin, and mole all anchored to that fixed number rather than the other way around.

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