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Einstein–de Haas Effect
The Einstein–de Haas effect is a physical phenomenon in which a change in the magnetic moment of a free body causes this body to rotate. The effect is a consequence of the conservation of angular momentum. It is strong enough to be observable in ferromagnetic materials. The experimental observation and accurate measurement of the effect demonstrated that the phenomenon of magnetization is caused by the alignment ( polarization) of the angular momenta of the electrons in the material along the axis of magnetization. These measurements also allow the separation of the two contributions to the magnetization: that which is associated with the spin from that which is due to the orbital motion of the electrons. The effect also demonstrated the close relation between the notions of angular momentum in classical and in quantum physics. The effect was predicted by O. W. Richardson in 1908. It is named after Albert Einstein and Wander Johannes de Haas, who published two papers in 1915 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetic Moment
In electromagnetism, the magnetic moment or magnetic dipole moment is the combination of strength and orientation of a magnet or other object or system that exerts a magnetic field. The magnetic dipole moment of an object determines the magnitude of torque the object experiences in a given magnetic field. When the same magnetic field is applied, objects with larger magnetic moments experience larger torques. The strength (and direction) of this torque depends not only on the magnitude of the magnetic moment but also on its orientation relative to the direction of the magnetic field. Its direction points from the south pole to the north pole of the magnet (i.e., inside the magnet). The magnetic moment also expresses the magnetic force effect of a magnet. The magnetic field of a magnetic dipole is proportional to its magnetic dipole moment. The dipole component of an object's magnetic field is symmetric about the direction of its magnetic dipole moment, and decreases as the inverse ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Torque
In physics and mechanics, torque is the rotational analogue of linear force. It is also referred to as the moment of force (also abbreviated to moment). The symbol for torque is typically \boldsymbol\tau, the lowercase Greek letter ''tau''. When being referred to as moment of force, it is commonly denoted by . Just as a linear force is a push or a pull applied to a body, a torque can be thought of as a twist applied to an object with respect to a chosen point; for example, driving a screw uses torque to force it into an object, which is applied by the screwdriver rotating around its axis to the drives on the head. Historical terminology The term ''torque'' (from Latin , 'to twist') is said to have been suggested by James Thomson and appeared in print in April, 1884. Usage is attested the same year by Silvanus P. Thompson in the first edition of ''Dynamo-Electric Machinery''. Thompson describes his usage of the term as follows: Today, torque is referred to using d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ampère Museum
The Ampère Museum is a museum of the history of electricity dedicated to André-Marie Ampère (1775–1836). The museum is located in Poleymieux-au-Mont-d'Or at approximately from Lyon by road and is housed in the house where André-Marie Ampère spent part of his youth. It was awarded the "Maisons des Illustres" (Illustrious house) label in 2013. The Ampère Museum has received the EPS historical site label (2021) awarded by the European Physical Society and the IEEE Historic Milestone label (2023) awarded by the Institute of Electrical and Electronics Engineers, IEEE. History In 1928, Hernand and Sosthenes Behn, American businessmen, of French origin by their mother, co-founders of the multinational company International Telephone and Telegraph, ITT, which at that time was developing its activities in France, on the advice of Paul Janet and as patrons of the arts, acquired the former Ampère property which had just been put up for sale. They donated it to the "Société fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geertruida De Haas-Lorentz
Geertruida Luberta "Berta" de Haas-Lorentz (20 November 1885 – 1973) was a Dutch physicist and a professor at the Delft University of Technology, Technical University of Delft. She was the first to theoretically study thermal fluctuations in electric circuits, treating Electron, electrons as Brownian motion, Brownian particles. Consequently she is considered one of the pioneers of Electronic noise, electrical noise theory. She was the daughter and doctoral student of Hendrik Lorentz. She went by the name Berta, or Ber. Life Berta Lorentz was born in Leiden, Netherlands, the eldest daughter of the physicist and 1902 Nobel Prize in Physics winner Hendrik Lorentz and . Berta was the eldest of four children. Her siblings were Johanna Wilhelmina (born 1889), Gerrit (born 1893, died 1894), and Rudolf (born 1895). At that time of her birth, her father was Professor of Theoretical Physics at the University of Leiden. Her mother, Aletta Kaiser, took care of the children and househol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dirac Equation
In particle physics, the Dirac equation is a relativistic wave equation derived by British physicist Paul Dirac in 1928. In its free form, or including electromagnetic interactions, it describes all spin-1/2 massive particles, called "Dirac particles", such as electrons and quarks for which parity is a symmetry. It is consistent with both the principles of quantum mechanics and the theory of special relativity, and was the first theory to account fully for special relativity in the context of quantum mechanics. The equation is validated by its rigorous accounting of the observed fine structure of the hydrogen spectrum and has become vital in the building of the Standard Model. The equation also implied the existence of a new form of matter, '' antimatter'', previously unsuspected and unobserved and which was experimentally confirmed several years later. It also provided a ''theoretical'' justification for the introduction of several component wave functions in Pauli' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Quincy Stewart
John Quincy Stewart (September 10, 1894 – March 19, 1972) was an American astrophysicist. He obtained his Ph.D. in physics from Princeton University in 1919. He taught astrophysics at Princeton from 1921 until he retired in 1963. Stewart was a civilian aeronautical engineer, an Army 1st Lieutenant, and later served as a chief instructor in the Army Engineering School, during World War I. He was later a research engineer in the American Telephone and Telegraph Company. He became interested in social physics in 1946, (first investigated in 1693 by astronomer Edmond Halley), demonstrating the use of physical laws in the area of social sciences, for example, demographic gravitation.Stewart, John Q., "Demographic Gravitation: Evidence and Applications", Sociometry, Vol. 11, No. 1/2. (February – May, 1948), pp. 31–5/ref> He co-wrote an influential two-volume textbook in 1927 with Raymond Smith Dugan and Henry Norris Russell Henry Norris Russell ForMemRS HFRSE F ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barnett Effect
The Barnett effect is the magnetization of an uncharged body when spun on its axis. It was discovered by American physicist Samuel Jackson Barnett, Samuel Barnett in 1915. An uncharged object rotating with angular velocity tends to spontaneously magnetize, with a magnetization given by : M = \chi \omega / \gamma, where is the gyromagnetic ratio for the material, is the magnetic susceptibility. The magnetization occurs parallel to the axis of spin. Barnett was motivated by a prediction by Owen Richardson in 1908, later named the Einstein–de Haas effect, that magnetizing a ferromagnet can induce a mechanical rotation. He instead looked for the opposite effect, that is, that spinning a ferromagnet could change its magnetization. He established the effect with a long series of experiments between 1908 and 1915. See also * London moment References Further reading * Magnetism {{CMP-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Samuel Jackson Barnett
Samuel Jackson Barnett (December 14, 1873 – May 22, 1956) was an American physicist. He was a professor at the University of California, Los Angeles. Barnett was born in Woodson County, Kansas, the son of a minister. In 1894, he received a B.A. in physics from the University of Denver and received his Ph.D. from Cornell University in 1898. From 1898 to 1918 he taught at several universities: Colorado College, Stanford University, Tulane University, and Ohio State University. In 1903 he published his book ''Elements of Electromagnetic Theory'', which he dedicated to his friend Professor Francis H. Smith at the University of Virginia. From 1918 to 1926 he worked at the Carnegie Institution for Science in Washington, DC. In 1926 he was a professor at the University of California at Los Angeles. Barnett worked mainly on electromagnetism, and discovered the Barnett effect. His wife, Mrs. Lelia Jefferson Harvie Barnett, was a scientific co-collaborator, and together they worked in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bohr Model
In atomic physics, the Bohr model or Rutherford–Bohr model was a model of the atom that incorporated some early quantum concepts. Developed from 1911 to 1918 by Niels Bohr and building on Ernest Rutherford's nuclear Rutherford model, model, it supplanted the plum pudding model of J. J. Thomson only to be replaced by the quantum atomic model in the 1920s. It consists of a small, dense nucleus surrounded by orbiting electrons. It is analogy, analogous to the structure of the Solar System, but with attraction provided by Coulomb's law, electrostatic force rather than gravity, and with the electron energies quantized (assuming only discrete values). In the history of atomic physics, it followed, and ultimately replaced, several earlier models, including Joseph Larmor's Solar System model (1897), Jean Perrin's model (1901), the Cubical atom, cubical model (1902), Hantaro Nagaoka's Saturnian model (1904), the plum pudding model (1904), Arthur Haas's quantum model (1910), the Ru ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Princeton University
Princeton University is a private university, private Ivy League research university in Princeton, New Jersey, United States. Founded in 1746 in Elizabeth, New Jersey, Elizabeth as the College of New Jersey, Princeton is the List of Colonial Colleges, fourth-oldest institution of higher education in the United States and one of the nine colonial colleges chartered before the American Revolution. The institution moved to Newark, New Jersey, Newark in 1747 and then to its Mercer County, New Jersey, Mercer County campus in Princeton nine years later. It officially became a university in 1896 and was subsequently renamed Princeton University. The university is governed by the Trustees of Princeton University and has an endowment of $37.7 billion, the largest List of colleges and universities in the United States by endowment, endowment per student in the United States. Princeton provides undergraduate education, undergraduate and graduate education, graduate instruction in the hu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gyromagnetic Ratio
In physics, the gyromagnetic ratio (also sometimes known as the magnetogyric ratio in other disciplines) of a particle or system is the ratio of its magnetic moment to its angular momentum, and it is often denoted by the symbol , gamma. Its SI unit is the reciprocal second per tesla (s−1⋅T−1) or, equivalently, the coulomb per kilogram (C⋅kg−1). The -factor of a particle is a related dimensionless value of the system, derived as the ratio of its gyromagnetic ratio to that which would be classically expected from a rigid body of which the mass and charge are distributed identically, and for which total mass and charge are the same as that of the system. For a classical rotating body Consider a nonconductive charged body rotating about an axis of symmetry. According to the laws of classical physics, it has both a magnetic dipole moment due to the movement of charge and an angular momentum due to the movement of mass arising from its rotation. It can be shown that as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Torsion Spring
A torsion spring is a spring that works by twisting its end along its axis; that is, a flexible elastic object that stores mechanical energy when it is twisted. When it is twisted, it exerts a torque in the opposite direction, proportional to the amount (angle) it is twisted. There are various types: *A torsion bar is a straight bar of metal or rubber that is subjected to twisting (shear stress) about its axis by torque applied at its ends. *A more delicate form used in sensitive instruments, called a torsion fiber consists of a fiber of silk, glass, or quartz under tension, that is twisted about its axis. *A helical torsion spring, is a metal rod or wire in the shape of a helix (coil) that is subjected to twisting about the axis of the coil by sideways forces (bending moments) applied to its ends, twisting the coil tighter. *Clocks use a spiral wound torsion spring (a form of helical torsion spring where the coils are around each other instead of piled up) sometimes ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
