The same situations that create magnetic fields—charge moving in a current or in an atom, and intrinsic magnetic dipoles—are also the situations in which a magnetic field has an effect, creating a force. Following is the formula for moving charge; for the forces on an intrinsic dipole, see magnetic dipole. When a charged particle moves through a magnetic field B , it feels a Lorentz force F given by the cross product : .
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Because this is a cross product, the force is perpendicular to both the motion of the particle and the magnetic field. It follows that the magnetic force does no work on the particle; it may change the direction of the particle's movement, but it cannot cause it to speed up or slow down. The magnitude of the force is. One tool for determining the direction of the velocity vector of a moving charge, the magnetic field, and the force exerted is labeling the index finger "V", the middle finger "B", and the thumb "F" with your right hand. When making a gun-like configuration, with the middle finger crossing under the index finger, the fingers represent the velocity vector, magnetic field vector, and force vector, respectively.
See also right-hand rule. A very common source of magnetic field found in nature is a dipole , with a " South pole " and a " North pole ", terms dating back to the use of magnets as compasses, interacting with the Earth's magnetic field to indicate North and South on the globe.
Since opposite ends of magnets are attracted, the north pole of a magnet is attracted to the south pole of another magnet. The Earth's North Magnetic Pole currently in the Arctic Ocean, north of Canada is physically a south pole, as it attracts the north pole of a compass. A magnetic field contains energy , and physical systems move toward configurations with lower energy.
Magnetism - Wikipedia
When diamagnetic material is placed in a magnetic field, a magnetic dipole tends to align itself in opposed polarity to that field, thereby lowering the net field strength. When ferromagnetic material is placed within a magnetic field, the magnetic dipoles align to the applied field, thus expanding the domain walls of the magnetic domains. Since a bar magnet gets its ferromagnetism from electrons distributed evenly throughout the bar, when a bar magnet is cut in half, each of the resulting pieces is a smaller bar magnet.
Even though a magnet is said to have a north pole and a south pole, these two poles cannot be separated from each other. A monopole—if such a thing exists—would be a new and fundamentally different kind of magnetic object. It would act as an isolated north pole, not attached to a south pole, or vice versa. Monopoles would carry "magnetic charge" analogous to electric charge. Despite systematic searches since , as of [update] , they have never been observed, and could very well not exist.
Nevertheless, some theoretical physics models predict the existence of these magnetic monopoles.
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Paul Dirac observed in that, because electricity and magnetism show a certain symmetry , just as quantum theory predicts that individual positive or negative electric charges can be observed without the opposing charge, isolated South or North magnetic poles should be observable. Using quantum theory Dirac showed that if magnetic monopoles exist, then one could explain the quantization of electric charge—that is, why the observed elementary particles carry charges that are multiples of the charge of the electron. Certain grand unified theories predict the existence of monopoles which, unlike elementary particles, are solitons localized energy packets.
The initial results of using these models to estimate the number of monopoles created in the Big Bang contradicted cosmological observations—the monopoles would have been so plentiful and massive that they would have long since halted the expansion of the universe.
However, the idea of inflation for which this problem served as a partial motivation was successful in solving this problem, creating models in which monopoles existed but were rare enough to be consistent with current observations. While heuristic explanations based on classical physics can be formulated, diamagnetism, paramagnetism and ferromagnetism can only be fully explained using quantum theory.
That this leads to magnetism is not at all obvious, but will be explained in the following. Here the last product means that a first electron, r 1 , is in an atomic hydrogen-orbital centered at the second nucleus, whereas the second electron runs around the first nucleus. This "exchange" phenomenon is an expression for the quantum-mechanical property that particles with identical properties cannot be distinguished.
It is specific not only for the formation of chemical bonds , but also for magnetism. That is, in this connection the term exchange interaction arises, a term which is essential for the origin of magnetism, and which is stronger, roughly by factors and even by , than the energies arising from the electrodynamic dipole-dipole interaction.
Electricity and Magnetism: Magnetic Fields and Forces
The " singlet state ", i. The tendency to form a homoeopolar chemical bond this means: the formation of a symmetric molecular orbital, i. In contrast, the Coulomb repulsion of the electrons, i. Thus, now the spins would be parallel ferromagnetism in a solid, paramagnetism in two-atomic gases. The last-mentioned tendency dominates in the metals iron , cobalt and nickel , and in some rare earths, which are ferromagnetic.
Most of the other metals, where the first-mentioned tendency dominates, are nonmagnetic e. Diatomic gases are also almost exclusively diamagnetic, and not paramagnetic. The Heitler-London considerations can be generalized to the Heisenberg model of magnetism Heisenberg The explanation of the phenomena is thus essentially based on all subtleties of quantum mechanics, whereas the electrodynamics covers mainly the phenomenology.
Some organisms can detect magnetic fields, a phenomenon known as magnetoception. In addition to detection, biomagnetic phenomena are utilized by organisms in a number of ways. For instance, chitons , a type of marine mollusk, produce magnetite to harden their teeth, and even humans produce magnetite in bodily tissue. From Wikipedia, the free encyclopedia. For other uses, see Magnetic disambiguation , Magnetism disambiguation , and Magnetized disambiguation.
Covariant formulation. Electromagnetic tensor stress—energy tensor. Main article: History of electromagnetism. See also: Magnetic moment. Main article: Diamagnetism.
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Main article: Paramagnetism. Main article: Ferromagnetism. Main article: Magnetic domains. Magnetic domains boundaries white lines in ferromagnetic material black rectangle. Main article: Antiferromagnetism. Main article: Ferrimagnetism. Main article: Superparamagnetism. Main article: Classical electromagnetism and special relativity.
What Is Magnetism? Definition, Examples, Facts
Play media. Main article: Magnetic field. Main article: Magnetic dipole. Main article: Magnetic monopole. SI electromagnetism units v t e. Coercivity Gravitomagnetism Magnetic hysteresis Magnetar Magnetic bearing Magnetic circuit Magnetic cooling Magnetic field viewing film Magnetic stirrer Magnetic structure Magnetism and temperature Micromagnetism Neodymium magnet Plastic magnet Rare-earth magnet Spin wave Spontaneous magnetization Vibrating-sample magnetometer.
Magnetism: Fundamentals. See, for example, "Magnet". Language Hat blog. Retrieved 22 March Retrieved CRC Press.
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