Fr.: équation de Fokker-Planck
A modified form of → Boltzmann's equation allowing for collision terms in an approximate way. It describes the rate of change of a particle's velocity as a result of small-angle collisional deflections.
After Dutch physicist Adriaan Fokker (1887-1972) and the German physicist Max Planck (1858-1947); → equation.
Short for Max Planck (1858-1947), German physicist, great authority on thermodynamics and creator of the quantum theory.
pâyâ-ye Planck (#)
Fr.: constante de Planck
A physical constant that determines the energy of quantum as a function of its frequency; symbol h. Also called → Planck's constant. On 16 November 2018, the International Bureau of Weights and Measures (BIPM) voted to redefine the kilogram by fixing the value of the Planck constant, thereby defining the kilogram in terms of the second and the speed of light. Starting 20 May 2019, the new value is exactly 6.626 070 15 × 10-34 J s. The → reduced Planck constant, ħ = h / 2π, is also called the → Dirac constant.
Fr.: courbe de Planck
Same as → blackbody curve.
Fr.: densité de Planck
The density corresponding to a → Planck mass in a cubic region of edge length given by the → Planck length: ρP = c5/(ħG2) ≅ 5.16 x 1093 g cm-3, where c is the → speed of light, ħ is the → reduced Planck's constant, and G is the → gravitational constant.
Fr.: distribution de Planck
The distribution of radiation with wavelength for a blackbody, given by → Planck's radiation law.
Fr.: énergie de Planck
The unit of energy in the system of Planck units. EP = √ (ħ c5/G) ≅ 1.22 x 1019 GeV. It can also be defined as EP = ħ / tP, where tP is the Planck time. This is an extraordinarily large amount of energy on the subatomic scale and particle accelerators have yet to produce a particle with this magnitude of energy. Understanding the properties of a subatomic particle that contains the Planck Energy is helpful in developing a Unified Field Theory which encompasses the realms of Quantum Theory and Relativity, although this too has evaded complete scientific understanding.
Fr.: ère de Planck
The first 10-43 seconds of the Universe's existence, when the size of the Universe was roughly the Planck length and during which quantum effects of gravity were significant. Also called Planck epoch. Our understanding of the Planck era is poor because theory which encompasses both quantum mechanics and general relativity is needed to be developed.
Fr.: fonction de Planck
Same as → Planck's blackbody formula.
derâzâ-ye Planck (#)
Fr.: longueur de Planck
The size limit, lP = √ (ħ G/ c3), about 10-33 cm, at which Einstein's notions of space-time are supposed to break down, and space is predicted to become "foam like."
Fr.: masse de Planck
The unit of mass in Planck's system of physical units, mP = √ (ħ c/ G) = 2.176 x 10-8 kg. It is also the mass of a black hole whose Compton wavelength is comparable to its Schwarzschild radius.
Fr.: postulat de Planck
The postulate that the energy of oscillators in a blackbody is quantized by E = nhν, where n = 1, 2, 3, ..., h is Planck's constant, and ν the frequency.
Fr.: Satellite Planck
A European Space Agency (ESA) mission to map the full sky in the 30 GHz to 1 THz range and to measure the → anisotropies of the → cosmic microwave background (CMB) with a sensitivity set by fundamental limits, i.e. photon noise and contamination by foregrounds. It was launched on 14 May 2009, together with the → Herschel Satellite. Its observing position is a halo orbit around the L2 → Lagrangian point, some 1.5 million km from Earth. Its → Gregorian-like off-axis telescope has an effective aperture of 1.5 m and images the sky on two sets of feed-horns. The Low Frequency Instrument (LFI, at frequencies 30, 44, 70 GHz) amplifies with High Electron Mobility Transistors cooled at 20 K the radiation collected by 13 horns. The High Frequency Instrument (HFI, at 100, 143, 217, 353, 545, 857 GHz) detects the shorter waves with 52 bolometers cooled at only 0.1 degree above the → absolute zero. Both instruments can detect both the total intensity and polarization of photons. The Planck mission is intended to provide maps with a sensitivity of a few micro-Kelvin and an angular resolution down to 5 arcmin, which is considered as a major improvement with respect to the Wilkinson Microwave Anisotropy Probe (→ WMAP) launched by the NASA in 2002. Planck will provide a major source of information relevant to several cosmological and astrophysical issues, such as testing theories of the early Universe and the origin of cosmic structure. It will also provide to astronomers 9 complete maps of the full sky at wavelengths from 0.3 mm to 1 cm, that complement the 4 maps taken by the → IRAS satellite in the 2.5 to 100 micrometer range.
Fr.: échelle de Plancck
Fr.: spectrum de Planck
Same as → blackbody spectrum.
Fr.: temps de Planck
The time representing the → Planck length divided by the → speed of light. It is expressed by: tP = (Għ/c5)1/2≅ 5.4 x 10-44 s, where G is the → gravitational constant, ħ is the → reduced Planck's constant, and c is the → speed of light. At the Planck time, the mass density of the Universe is thought to approach the → Planck density.
yekâhâ-ye Planck (#)
Fr.: unités de Planck
A set of → natural units in which the normalized units are: the gravitational constant, Planck's constant, the speed of light, the Coulomb constant, and Boltzmann's constant.
Planck's blackbody formula
disul-e siyah jesm-e Planck
Fr.: formule du corps noir de Planck
A formula that determines the distribution of intensity of radiation that prevails under conditions of thermal equilibrium at a temperature T: Bv = (2hν3 / c2)[exp(hν / kT) - 1]-1 where h is Planck's constant and ν is the frequency.
pâyâ-ye Planck (#)
Fr.: constante de Planck
Planck's radiation law
qânun-e tâbeš-e Planck
Fr.: loi du rayonnement de Planck
An equation that expresses the energy radiated per unit area per unit time per unit wavelength range by a blackbody as a function of temperature. It is expressed by → Planck's blackbody formula.