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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: =.
The de Broglie wavelength is the wavelength, λ, associated with a particle with momentum p through the Planck constant, h: =. Wave-like behavior of matter has been experimentally demonstrated, first for electrons in 1927 and for other elementary particles, neutral atoms and molecules in the years since.
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.
For example, a wavenumber in inverse centimeters can be converted to a frequency expressed in the unit gigahertz by multiplying by 29.979 2458 cm/ns (the speed of light, in centimeters per nanosecond); [5] conversely, an electromagnetic wave at 29.9792458 GHz has a wavelength of 1 cm in free space.
where ω is the angular frequency and k is the wavevector with magnitude | k | = k, equal to the wave number, the energy–momentum relation can be expressed in terms of wave quantities: ( ℏ ω ) 2 = ( c ℏ k ) 2 + ( m 0 c 2 ) 2 , {\displaystyle \left(\hbar \omega \right)^{2}=\left(c\hbar k\right)^{2}+\left(m_{0}c^{2}\right)^{2}\,,}
The top electron has twice the momentum, while the bottom electron has half. Note that as the momentum increases, the phase velocity decreases down to c, whereas the group velocity increases up to c, until the wave packet and its phase maxima move together near the speed of light, whereas the wavelength continues to decrease without bound. Both ...
In 1900, Max Planck postulated the proportionality between the frequency of a photon and its energy , =, [11] [12] and in 1916 the corresponding relation between a photon's momentum and wavelength, =, [13] where is the Planck constant.
In Newtonian mechanics, momentum (pl.: momenta or momentums; more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. . It is a vector quantity, possessing a magnitude and a directi