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The Planck constant, or Planck's constant, denoted by , 1 is a fundamental physical constant 1 of foundational importance in quantum mechanics: a photon 's energy is equal to its frequency multiplied by the Planck constant, and the wavelength of a matter wave equals the Planck constant divided by the associated particle momentum.
This equation is known as the Planck relation. Additionally, using equation f = c/λ, = where E is photon energy; λ is the photon's wavelength; c is the speed of light in a vacuum; h is the Planck constant; The photon energy at 1 Hz is equal to 6.626 070 15 × 10 −34 J, which is equal to 4.135 667 697 × 10 −15 eV.
Planck units. hide. In particle physics and physical cosmology, Planck units are a system of units of measurement defined exclusively in terms of four universal physical constants: c, G, ħ, and kB (described further below). Expressing one of these physical constants in terms of Planck units yields a numerical value of 1.
The Planck relation [1] [2] [3] (referred to as Planck's energy–frequency relation, [4] the Planck–Einstein relation, [5] Planck equation, [6] and Planck formula, [7] though the latter might also refer to Planck's law [8] [9]) is a fundamental equation in quantum mechanics which states that the energy E of a photon, known as photon energy, is proportional to its frequency ν: =.
e. In physics, the fine-structure constant, also known as the Sommerfeld constant, commonly denoted by α (the Greek letter alpha), is a fundamental physical constant which quantifies the strength of the electromagnetic interaction between elementary charged particles. It is a dimensionless quantity, independent of the system of units used ...
Planck considered only the units based on the universal constants G, h, c, and k B to arrive at natural units for length, time, mass, and temperature, but no electromagnetic units. [7] The Planck system of units is now understood to use the reduced Planck constant, ħ, in place of the Planck constant, h. [8]
The elementary charge, usually denoted by e, is a fundamental physical constant, defined as the electric charge carried by a single proton or, equivalently, the magnitude of the negative electric charge carried by a single electron, which has charge −1 e. [ 2 ][ a ] In the SI system of units, the value of the elementary charge is exactly ...
where c is the speed of light and h is the Planck constant. [4] The relative uncertainty, 5 × 10 −8 in the 2006 CODATA recommended value, [5] is due entirely to the uncertainty in the value of the Planck constant. With the re-definition of kilogram in 2019, there is no uncertainty by definition left in Planck constant anymore.