Magnetic fields surround magnetic materials and electric currents Electric current means, depending on the context, a flow of electric charge or the rate of flow of electric charge (a quantity). This flowing electric charge is typically carried by moving electrons, in a conductor such as wire; in an electrolyte, it is instead carried by ions, and, in a plasma, by both and are detected by the force they exert on other magnetic materials and moving electric charges Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields. The interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field In mathematics a vector field is a construction in vector calculus which associates a vector to every point in a subset of Euclidean space.[1]
For the physics of magnetic materials, see magnetism Magnetism, a non-contact force, is a category of behaviour of materials that respond at an atomic or subatomic level to an applied magnetic field. For example, the most well known form of magnetism is ferromagnetism such that some ferromagnetic materials produce their own persistent magnetic field. However, all materials are influenced to greater and magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials like iron and attracts or repels other magnets, more specifically ferromagnetism Ferromagnetism is the basic mechanism by which certain materials form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished. Ferromagnetism is the strongest type; it is the only type that can produce forces strong enough to be felt, and is responsible for the common phenomena of, paramagnetism Paramagnetism is a form of magnetism that occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields and hence have a relative magnetic permeability of ≥1 . The magnetic moment induced by the applied field is linear in the field strength and rather weak. It typically requires a, and diamagnetism Diamagnetism is the property of an object which causes it to create a magnetic field in opposition to an externally applied magnetic field, thus causing a repulsive effect. Specifically, an external magnetic field alters the orbital velocity of electrons around their nuclei, thus changing the magnetic dipole moment in the direction opposing the. For constant magnetic fields, such as are generated by magnetic materials and steady currents, see magnetostatics Magnetostatics is the study of static magnetic fields. In electrostatics, the charges are stationary, whereas here, the currents are steady or dc. As it turns out magnetostatics is a good approximation even when the currents are not static as long as the currents do not alternate rapidly. A changing magnetic field generates an electric field In physics, an electric field is a property that describes the space that surrounds electrically charged particles or that which is in the presence of a time-varying magnetic field. This electric field exerts a force on other electrically charged objects. The concept of an electric field was introduced by Michael Faraday and a changing electric field results in a magnetic field. (See electromagnetism Electromagnetism is one of the four fundamental interactions of nature, along with strong interaction, weak interaction and gravitation. It is the force that causes the interaction between electrically charged particles; the areas in which this happens are called electromagnetic fields.)
In view of special relativity Special relativity (also known as the special theory of relativity or STR) is the physical theory of measurement in inertial frames of reference proposed in 1905 by Albert Einstein (after the considerable and independent contributions of Hendrik Lorentz, Henri Poincaré and others) in the paper "On the Electrodynamics of Moving Bodies", the electric and magnetic fields are two interrelated aspects of a single object, called the electromagnetic field The electromagnetic field is a physical field produced by electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction. It is one of the four fundamental forces of nature (the others are. A pure electric field in one reference frame A frame of reference in physics, may refer to a coordinate system or set of axes within which to measure the position, orientation, and other properties of objects in it, or it may refer to an observational reference frame tied to the state of motion of an observer. It may also refer to both an observational reference frame and an attached is observed as a combination of both an electric field and a magnetic field in a moving reference frame.
In quantum physics, the pure magnetic (and electric) fields are understood to be effects caused by virtual photons; in the language of the Standard Model The Standard Model of particle physics is a theory concerning the electromagnetic, weak and strong nuclear interactions which mediate the dynamics of the known subatomic particles. Developed throughout the early and middle 20th century, the current formulation was finalized in the mid 1970s upon experimental confirmation of the existence of quarks the electromagnetic force in all of its manifestations is mediated by photons. Most often this microscopic description is not needed because the simpler classical theory covered in this article is sufficient; the difference is negligible under the low field energies of most circumstances.
B and H
See also: Magnetization Here, N is the number of magnetic moments in the sample. The quantity N/V is usually written as n, the number density of magnetic moments. The M-field is measured in amperes per meter in SI unitsThe term magnetic field is used for two different vector fields, denoted B and H.[2] There are many alternative names for both, though (see sidebar). To avoid confusion, this article uses B-field and H-field for these fields, and uses magnetic field where either or both fields apply.
The B-field can be defined in many equivalent ways based on the effects it has on its environment. For instance, a particle having an electric charge Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields. The interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the, q, and moving in a B-field with a velocity In physics, velocity is the rate of change of displacement . It is a vector physical quantity; both magnitude and direction are required to define it. The scalar absolute value (magnitude) of velocity is speed, a quantity that is measured in meters per second (m/s or ms−1) when using the SI (metric) system, v, experiences a force, F, called the Lorentz force In physics, the Lorentz force is the force on a point charge due to electromagnetic fields. It is given by the following equation in terms of the electric and magnetic fields: (see below). In SI The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. It is the world's most widely used system of measurement, both in everyday commerce and in science units, the Lorentz force equation is
where × is the vector cross product In mathematics, the cross product is a binary operation on two vectors in a three-dimensional Euclidean space that results in another vector which is perpendicular to the plane containing the two input vectors. The algebra defined by the cross product is neither commutative nor associative. It contrasts with the dot product which produces a scalar. The B-field is measured in teslas The tesla is the SI derived unit of magnetic field B (which is also known as "magnetic flux density" and "magnetic induction"). One tesla is equal to one weber per square meter, and it was defined in 1960 in honor of the Yugoslavian-American inventor, physicist, and electrical engineer Nikola Tesla. One billionth of a tesla is in SI The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. It is the world's most widely used system of measurement, both in everyday commerce and in science units and in gauss in cgs The centimetre-gram-second system is a metric system of physical units based on centimetre as the unit of length, gram as a unit of mass, and second as a unit of time. All CGS mechanical units are unambiguously derived from these three base units, but there are several different ways of extending the CGS system to cover electromagnetism units.
An alternate working definition of the B-field can be given in terms of the torque Torque, also called moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist on a magnetic dipole placed in a B-field:
Although views have shifted over the years, B is now understood as being the fundamental quantity A set of fundamental units is a set of units for physical quantities from which every other unit can be generated, while H is a derived field[citation needed]. H is defined as a modification of B due to magnetic fields produced by material media, such that (in SI The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. It is the world's most widely used system of measurement, both in everyday commerce and in science):
where M is the magnetization Here, N is the number of magnetic moments in the sample. The quantity N/V is usually written as n, the number density of magnetic moments. The M-field is measured in amperes per meter in SI units of the material and μ0 is the permeability of free space (or magnetic constant).[3] The H-field is measured in amperes The ampere is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère (1775–1836), French mathematician and physicist, considered the father of electrodynamics. In practice, its name is often shortened to amp per meter The metre , symbol m, is the base unit of length in the International System of Units (SI). Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole, its definition has been periodically refined to reflect growing knowledge of metrology. Since 1983, it is defined as the distance travelled by light in (A/m) in SI units The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. It is the world's most widely used system of measurement, both in everyday commerce and in science, and in oersteds (Oe) in cgs units.[4]
In materials for which M is proportional to B the relationship between B and H can be cast into the simpler form: H = B/μ, where μ is a material dependent parameter called the permeability In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. Magnetic permeability is typically represented by the Greek letter μ. The term was coined in September, 1885 by Oliver Heaviside. The reciprocal of magnetic permeability is magnetic reluctivity. In free space In classical physics, free space is a concept of electromagnetic theory, corresponding to a theoretically perfect vacuum and sometimes referred to as the vacuum of free space, or as classical vacuum, and is appropriately viewed as a reference medium, there is no magnetization, M, so that H = B/μ0. For many materials, though, there is no simple relationship between B and M. For example, ferromagnetic Ferromagnetism is the basic mechanism by which certain materials form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished. Ferromagnetism is the strongest type; it is the only type that can produce forces strong enough to be felt, and is responsible for the common phenomena of materials and superconductors Superconductivity is an electrical resistance of exactly zero which occurs in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes in 1911. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It is also characterized by a phenomenon called the Meissner have a magnetization that is a multiple-valued function of B due to hysteresis Hysteresis refers to systems that have memory, where the effects of the current input to the system are experienced with a certain delay in time. Such a system may exhibit path dependence, or "rate-independent memory" . Hysteresis phenomena occur in magnetic materials, ferromagnetic materials and ferroelectric materials, as well as in.[5]
See History below for further discussion.
The magnetic field and permanent magnets
Main articles: Magnetic moment The magnetic moment of a magnet is a measure of its tendency to align with a magnetic field. Both the magnetic moment and magnetic field may be considered to be vectors having a magnitude and direction. The direction of the magnetic moment points from the south to north pole of a magnet. The magnetic field produced by a magnet is proportional to and Magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials like iron and attracts or repels other magnetsPermanent magnets A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials and attracts or repels other magnets are objects that produce their own persistent magnetic fields. All permanent magnets have both a north and a south pole. They are made of ferromagnetic Ferromagnetism is the basic mechanism by which certain materials form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished. Ferromagnetism is the strongest type; it is the only type that can produce forces strong enough to be felt, and is responsible for the common phenomena of materials such as iron Iron is the most common element in the earth as a whole, and the fourth most common in the Earth's crust. It is produced as a result of stellar fusion in high-mass stars, and it is the heaviest stable element produced by stellar fusion because the fusion of iron is the last nuclear fusion reaction that is exothermic. Iron is the most widely used and nickel that have been magnetized. The strength of a magnet is represented by its magnetic moment, m; for simple magnets, m points in the direction of a line drawn from the south to the north pole of the magnet. For more details about magnets see magnetization below and the article ferromagnetism.
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Fri, 16 Jul 2010 18:36:04 GMT+00:00
storms and young volcanoes :Study reveals White Hat News Mercury's magnetic field also called magnetosphere, apparently releases energy in violent magnetic disturbances called substorms. ...
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hu, 08 Jun 2006 04:57:00 GM
Magnetic field. lines at the surface of Tau Scorpii. Image credit: MM Jardine/JF Donati. Click to enlarge Our Sun can send out its share of solar.
Q. Does an electric motor run because of magnetic field or electric field ? Will an electric field exert a force on a magnet (attraction or repulsion) ? Is it a magnetic field or an electric field which when crosses a conductor generate electric current in it ? Are electromagnetic waves same as electromagnetic field ?
Asked by Rox Tarr - Wed May 19 22:45:54 2010 - - 1 Answers - 0 Comments
