|
Femtometre
The femtometre (American spelling femtometer), symbol fm, (derived from the Danish and Norwegian word 'fifteen', ) is a unit of length in the International System of Units (SI) equal to 10−15 metres, which means a quadrillionth of one metre. This distance is sometimes called a fermi and was so named in honour of Italian naturalized to American physicist Enrico Fermi, as it is a typical length-scale of nuclear physics. Definition and equivalents 1000000 zeptometres = 1 femtometre = 1 fermi = 0.000001 nanometre = femtometres = 1 millimetre. For example, the charge radius of a proton is approximately 0.841 femtometres while the radius of a gold nucleus is approximately 8.45 femtometres. 1 barn = 100 fm2 History The femtometre was adopted by the 11th ''Conférence Générale des Poids et Mesures'', and added to the SI in 1964, using the Danish word for "15" and the similarity in spelling with ''fermi''. The fermi is named after the It ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zeptometre
The following are examples of orders of magnitude for different lengths. Overview Detailed list To help compare different orders of magnitude, the following list describes various lengths between 1.6 \times 10^ metres and 10^metres. Subatomic scale Atomic to cellular scale Cellular to human scale Human to astronomical scale Astronomical scale 1 quectometre and less The ' ( SI symbol: ') is a unit of length in the metric system equal to . To help compare different orders of magnitude, this section lists lengths shorter than 10−30 m (1 qm). *1.6 × 10−5 quectometres (1.6 × 10−35 metres) – the Planck length (Measures of distance shorter than this do not make physical sense, according to current theories of physics.) *1 qm – 1 quectometre, the smallest named subdivision of the metre in the SI base unit of length, one nonillionth of a metre. 1 rontometre The ' ( SI symbol: ') is a unit of length in the metric system equal to . *1 rm – 1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Charge Radius
The rms charge radius is a measure of the size of an atomic nucleus, particularly the proton distribution. The proton radius is about one femtometre = . It can be measured by the scattering of electrons by the nucleus. Relative changes in the mean squared nuclear charge distribution can be precisely measured with atomic spectroscopy. Definition The problem of defining a radius for the atomic nucleus has some similarity to that of defining a radius for the entire atom; neither has well defined boundaries. However, basic liquid drop models of the nucleus imagine a fairly uniform density of nucleons, theoretically giving a more recognizable surface to a nucleus than an atom, the latter being composed of highly diffuse electron clouds with density gradually reducing away from the centre. For individual protons and neutrons or small nuclei, the concepts of size and boundary can be less clear. A single nucleon needs to be regarded as a " color confined" bag of three valence quark ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metre
The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of of a second, where the second is defined by a hyperfine transition frequency of caesium. The metre was originally defined in 1791 by the French National Assembly as one ten-millionth of the distance from the equator to the North Pole along a great circle, so the Earth's polar circumference is approximately . In 1799, the metre was redefined in terms of a prototype metre bar. The bar used was changed in 1889, and in 1960 the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86. The current definition was adopted in 1983 and modified slightly in 2002 to clarify that the metre is a measure of proper length. From 1983 until 2019, the metre was formally defined as the length of the pat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atomic Nucleus
The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford at the Department_of_Physics_and_Astronomy,_University_of_Manchester , University of Manchester based on the 1909 Geiger–Marsden experiments, Geiger–Marsden gold foil experiment. After the discovery of the neutron in 1932, models for a nucleus composed of protons and neutrons were quickly developed by Dmitri Ivanenko and Werner Heisenberg. An atom is composed of a positively charged nucleus, with a cloud of negatively charged electrons surrounding it, bound together by electrostatic force. Almost all of the mass of an atom is located in the nucleus, with a very small contribution from the electron cloud. Protons and neutrons are bound together to form a nucleus by the nuclear force. The diameter of the nucleus is in the range of () for hydrogen (the diameter of a single proton) to about for uranium. These dimensions are much ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Meter
The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of of a second, where the second is defined by a hyperfine transition frequency of caesium. The metre was originally defined in 1791 by the French National Assembly as one ten-millionth of the distance from the equator to the North Pole along a great circle, so the Earth's polar circumference is approximately . In 1799, the metre was redefined in terms of a prototype metre bar. The bar used was changed in 1889, and in 1960 the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86. The current definition was adopted in 1983 and modified slightly in 2002 to clarify that the metre is a measure of proper length. From 1983 until 2019, the metre was formally defined as the length of the path t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bohr Radius
The Bohr radius () is a physical constant, approximately equal to the most probable distance between the nucleus and the electron in a hydrogen atom in its ground state. It is named after Niels Bohr, due to its role in the Bohr model of an atom. Its value is The number in parentheses denotes the uncertainty of the last digits. Definition and value The Bohr radius is defined as a_0 = \frac = \frac , where * \varepsilon_0 is the permittivity of free space, * \hbar is the reduced Planck constant, * m_ is the mass of an electron, * e is the elementary charge, * c is the speed of light in vacuum, and * \alpha is the fine-structure constant. The CODATA value of the Bohr radius (in SI units) is History In the Bohr model for atomic structure, put forward by Niels Bohr in 1913, electrons orbit a central nucleus under electrostatic attraction. The original derivation posited that electrons have orbital angular momentum in integer multiples of the reduced Planck ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proton
A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an electron (the proton-to-electron mass ratio). Protons and neutrons, each with a mass of approximately one Dalton (unit), dalton, are jointly referred to as ''nucleons'' (particles present in atomic nuclei). One or more protons are present in the Atomic nucleus, nucleus of every atom. They provide the attractive electrostatic central force which binds the atomic electrons. The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number (represented by the symbol ''Z''). Since each chemical element, element is identified by the number of protons in its nucleus, each element has its own atomic number, which determines the number of atomic electrons and consequently the chemical characteristi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Length
Length is a measure of distance. In the International System of Quantities, length is a quantity with Dimension (physical quantity), dimension distance. In most systems of measurement a Base unit (measurement), base unit for length is chosen, from which all other units are derived. In the International System of Units (SI) system, the base unit for length is the metre. Length is commonly understood to mean the most extended size, dimension of a fixed object. However, this is not always the case and may depend on the position the object is in. Various terms for the length of a fixed object are used, and these include height, which is vertical length or vertical extent, width, breadth, and depth. ''Height'' is used when there is a base from which vertical measurements can be taken. ''Width'' and ''breadth'' usually refer to a shorter dimension than ''length''. ''Depth'' is used for the measure of a third dimension. Length is the measure of one spatial dimension, whereas area ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Particle Physics
Particle physics or high-energy physics is the study of Elementary particle, fundamental particles and fundamental interaction, forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the scale of protons and neutrons, while the study of combinations of protons and neutrons is called nuclear physics. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) and bosons (force-carrying particles). There are three Generation (particle physics), generations of fermions, although ordinary matter is made only from the first fermion generation. The first generation consists of Up quark, up and down quarks which form protons and neutrons, and electrons and electron neutrinos. The three fundamental interactions known to be mediated by bosons are electromagnetism, the weak interaction, and the strong interaction. Quark, Quarks cannot exist on their own but form hadrons. Hadrons that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reviews Of Modern Physics
''Reviews of Modern Physics'' (often abbreviated RMP) is a quarterly Peer review, peer-reviewed scientific journal published by the American Physical Society. It was established in 1929 and the current editor-in-chief is Michael Thoennessen. The journal publishes review articles, usually by established researchers, on all aspects of physics and related fields. The reviews are usually accessible to non-specialists and serve as introductory material to graduate students, which survey recent work, discuss key problems to be solved and provide perspectives toward the end. The journal has published several historically significant papers on quantum foundations, as well as the development of the Standard Model of particle physics. References External links * Academic journals established in 1929 Physics review journals Quarterly journals English-language journals American Physical Society academic journals {{physics-journal-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Robert Hofstadter
Robert Hofstadter (February 5, 1915 – November 17, 1990) was an American physicist. He was the joint winner of the 1961 Nobel Prize in Physics (together with Rudolf Mössbauer) "for his pioneering studies of electron scattering in atomic nuclei and for his consequent discoveries concerning the structure of nucleons".R. W. McAllister & Robert Hofstadter, "Elastic Scattering of 188 MeV Electrons from Proton and the Alpha Particle," ''Physical Review'', V102, p. 851 (1956). including his Nobel Lecture, December 11, 1961 ''The Electron-Scattering Method and Its Application to the Structure of Nuclei and Nucleons'' Biography Hofstadter was born in New York City on February 5, 1915, to Polish Jewish immigrants Louis Hofstadter, a salesman, and Henrietta, née Koenigsberg. He attended elementary and high schools in New York City and entered City College of New York, graduating with a B.S. degree ''magna cum laude'' in 1935 at the age of 20, and was awarded the Kenyon Prize in Mat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
