1900 – Max Planck discovers the law of black-body radiation (Planck’s law).
Planck’s law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature T. The law is named after Max Planck, who proposed it in 1900. It is a pioneering result of modern physics and quantum theory.
The spectral radiance of a body, Bν, describes the amount of energy it gives off as radiation of different frequencies. It is measured in terms of the power emitted per unit area of the body, per unit solid angle that the radiation is measured over, per unit frequency. Planck showed that the spectral radiance of a body for frequency ν at absolute temperature T is given by
B ν ( ν , T ) = 2 h ν 3 c 2 1 e h ν k B T − 1 {\displaystyle B_{\nu }(\nu ,T)={\frac {2h\nu ^{3}}{c^{2}}}{\frac {1}{e^{\frac {h\nu }{k_{\mathrm {B} }T}}-1}}} {\displaystyle B_{\nu }(\nu ,T)={\frac {2h\nu ^{3}}{c^{2}}}{\frac {1}{e^{\frac {h\nu }{k_{\mathrm {B} }T}}-1}}}
where kB the Boltzmann constant, h the Planck constant, and c the speed of light in the medium, whether material or vacuum.[1][2][3] The spectral radiance can also be measured per unit wavelength λ instead of per unit frequency. In this case, it is given by
B λ ( λ , T ) = 2 h c 2 λ 5 1 e h c λ k B T − 1 {\displaystyle B_{\lambda }(\lambda ,T)={\frac {2hc^{2}}{\lambda ^{5}}}{\frac {1}{e^{\frac {hc}{\lambda k_{\mathrm {B} }T}}-1}}} {\displaystyle B_{\lambda }(\lambda ,T)={\frac {2hc^{2}}{\lambda ^{5}}}{\frac {1}{e^{\frac {hc}{\lambda k_{\mathrm {B} }T}}-1}}}.
The law may also be expressed in other terms, such as the number of photons emitted at a certain wavelength, or the energy density in a volume of radiation. The SI units of Bν are W·sr−1·m−2·Hz−1, while those of Bλ are W·sr−1·m−3.
In the limit of low frequencies (i.e. long wavelengths), Planck’s law tends to the Rayleigh–Jeans law, while in the limit of high frequencies (i.e. small wavelengths) it tends to the Wien approximation.
Max Planck developed the law in 1900 with only empirically determined constants, and later showed that, expressed as an energy distribution, it is the unique stable distribution for radiation in thermodynamic equilibrium.[4] As an energy distribution, it is one of a family of thermal equilibrium distributions which include the Bose–Einstein distribution, the Fermi–Dirac distribution and the Maxwell–Boltzmann distribution.
Max Karl Ernst Ludwig Planck, FRS[2] (/plɑːŋk/;[3] 23 April 1858 – 4 October 1947) was a German theoretical physicist whose discovery of energy quanta won him the Nobel Prize in Physics in 1918.[4]
Planck made many contributions to theoretical physics, but his fame as a physicist rests primarily on his role as the originator of quantum theory, which revolutionized human understanding of atomic and subatomic processes. In 1948 the German scientific institution the Kaiser Wilhelm Society (of which Planck was twice president), was renamed the Max Planck Society (MPS). The MPS now includes 83 institutions representing a wide range of scientific directions.
1923 – Ruth Carter Stevenson, American art collector, founded the Amon Carter Museum of American Art (d. 2013)
Ruth Carter Stevenson (October 19, 1923 – January 6, 2013) was an American patron of the arts and founder of the Amon Carter Museum of American Art, which opened in Fort Worth, Texas, in January 1961.[1]
Stevenson was born to Amon G. Carter and Nenetta Carter in Fort Worth, Texas, in 1923.[2] She was the second daughter of Carter, the creator and publisher of the Fort Worth Star-Telegram.[1] She graduated from Sarah Lawrence College in Yonkers, New York, in 1945, as a chemistry major.[2][3]
Her father specified in his will that a museum specializing in Western American art to be created after his death in 1955,[1] to house his more than 700 art objects depicting the American West, primarily paintings and sculptures by Frederic Remington and Charles Russell.[2] Stevenson hired architect Philip Johnson to design the building and opened the Amon Carter Museum of Western Art in January 1961, following her father’s wishes.[1][3] She was the first president of the museum’s board of trustees and was president at her death in 2013.[4][5]
Stevenson was also the first woman to be appointed to the board of directors of the National Gallery of Art in Washington, D.C.,[1] and the first woman to become the chairman of that board.[3] Along with local art enthusiasts Owen Day and Sam Cantey III, Stephenson assembled An Art Exhibition for the President and Mrs. John F. Kennedy which decorated the suite in the Hotel Texas in Fort Worth, Texas, occupied by United States President John F. Kennedy and Jacqueline Kennedy on the night before his assassination on November 22, 1963.[6]
Ruth Carter Stevenson died at her home in Fort Worth, Texas, on January 6, 2013, at the age of 89.[1]
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- Wikimedia Commons picture of the day for December 5 December 5, 2024Picture of the day Trier, Alter Krahn on the Mosel.
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