 Current flowing through a wire produces a magnetic field ( B, labeled M here) around the wire. The field is oriented according to the right-hand rule. - For other senses of this term, see magnetic field (disambiguation).
In physics, a magnetic field is relativistic part of electric field (as explained by Einstein in 1905). When electric charge is moving by observer, the electric field of this charge due to space contraction no longer seen by the observer as spherically symmetric (nor even as radial) but must be computed using Lorentz transformations. One of products of these transformations is the part of electric field which only acts on moving charges - and we call it "magnetic field". Image File history File links Please see the file description page for further information. ...
It has been suggested that this article or section be merged into Magnetic field. ...
Illustration of a magnetic field around a wire through which current is flowing. ...
Illustration of a magnetic field around a wire through which current is flowing. ...
In mathematics and physics, the right-hand rule is a convention for determining relative directions of certain vectors. ...
Magnetic field can refer to: A magnetic field, the physical phenomenon produced by moving electric charges and exhibited by ferrous materials. ...
A Superconductor demonstrating the Meissner Effect. ...
In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. ...
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Relativistic effect of apparent contraction of coordinates of moving reference frame in the direction of motion when seen from non moving refernce frame. ...
The Lorentz transformation (LT), named after its discoverer, the Dutch physicist and mathematician Hendrik Antoon Lorentz (1853-1928), forms the basis for the special theory of relativity, which has been introduced to remove contradictions between the theories of electromagnetism and classical mechanics. ...
The quantum-mechanical motion of electrons in atoms produces magnetic fields of permanent ferromagnets. Spinning charged particles also have magnetic moment. Some electrically neutral particles (like neutron) with non-zero spin also have magnetic moment due to charge distribution in their inner structure. Spin-zero particles never have magnetic moment. A simple introduction to this subject is provided in Basics of quantum mechanics. ...
Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ...
The terms spin and SPIN have several meanings, including those primarily discussed as spinning: For spin in sub-atomic physics, see spin (physics) For the stalled aircraft maneuver or any of several forms of loss of control in aircraft, see spin (flight) For the periodical, see Spin Magazine For the...
In physics, the magnetic moment or magnetic dipole moment is a measure of the strength of a magnetic source. ...
Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ...
A magnetic field is a vector field: it associates with every point in space a (pseudo-)vector that may vary in time. The direction of the field is the equilibrium direction of a compass needle (=magnetic dipole) placed in the field. Vector field given by vectors of the form (-y, x) In mathematics a vector field is a construction in vector calculus which associates a vector to every point in a Euclidean space. ...
In physics and mathematics, a pseudovector (or axial vector) is a quantity that transforms like a vector under a proper rotation, but gains an additional sign flip under an improper rotation (a transformation that can be expressed as an inversion followed by a proper rotation). ...
In physics and in vector calculus, a spatial vector is a concept characterized by a magnitude, which is a scalar, and a direction (which can be defined in a 3-dimensional space by the Euler angles). ...
Compass in a wooden box A compass (or mariners compass) is a navigational instrument for finding directions on the earth. ...
The Earths magnetic field, which is approximately a dipole. ...
Symbols and terminology
Magnetic field is usually denoted by the symbol  . Historically, was called the magnetic flux density or magnetic induction. A distinct quantity,  , was called the magnetic field, and this terminology is still often used to distinguish the two in the context of magnetic materials (non-trivial permeability μ). Otherwise, however, this distinction is often ignored, and both quantities are frequently referred to as "the magnetic field." (Some authors call H the auxiliary field, instead.) In linear materials, such as air or free space, the two quantities are linearly related: Magnetic field density, otherwise known as magnetic flux density, is essentially what the layman knows as a magnetic field - akin to a gravitational or electric field. ...
In electromagnetism, permeability is the degree of magnetisation of a material that responds linearly to an applied magnetic field. ...
 where  is the magnetic permeability (in henries per meter) of the medium. In electromagnetism, permeability is the degree of magnetisation of a material that responds linearly to an applied magnetic field. ...
The henry (symbol H) is the SI unit of inductance. ...
The metre, or meter (symbol: m) is the SI base unit of length. ...
In SI units, and  are measured in teslas (T) and amperes per meter (A/m), respectively; or, in cgs units, in gauss (G) and oersteds (Oe), respectively. Two parallel wires carrying an electric current in the same sense will generate a magnetic field which will cause a force of attraction to each other. This fact is used to generate the value of an ampere of electric current. Note that while like charges repel and unlike ones attract, the opposite holds for currents: if the current in one of the two parallel wires is reversed, the two will repel. Cover of brochure The International System of Units. ...
The tesla (symbol T) is the SI derived unit of magnetic flux density (or magnetic induction). ...
The ampere (symbol: A) is the SI base unit of electric current equal to one coulomb per second. ...
The metre, or meter (symbol: m) is the SI base unit of length. ...
CGS is an acronym for centimetre-gram-second. ...
The gauss, abbreviated as G, is the cgs unit of magnetic flux density or magnetic induction (B), named after the German mathematician and physicist Carl Friedrich Gauss. ...
The oersted is old CGS unit of magnetic field strength (or magnetic induction). ...
The ampere (symbol: A) is the SI base unit of electric current equal to one coulomb per second. ...
Definition Lorentz transformation of spherically symmetric proper electric field E of moving electric charge (for example, electric field of an electron moving in a conducting wire) from charge's reference frame to non-moving observer's reference frame results in the following term: Proper in control theory Proper denotes a transfer function where the degree of the numerator does not exceed the degree of the denominator. ...
In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. ...
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Properties The electron is a lightweight fundamental subatomic particle that carries a negative electric charge. ...
 which we label as "magnetic field" and use the symbol B for it for the sake of mathematical simplicity.
As seen from the definition, the unit of magnetic field is newton-second per coulomb-meter (or newton per ampere-meter) and is called the tesla. The tesla (symbol T) is the SI derived unit of magnetic flux density (or magnetic induction). ...
Like the electric field, the magnetic field exerts force on electric charge—but only on moving charge: In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. ...
In physics, a net force acting on a body causes that body to accelerate; that is, to change its velocity. ...
 where - F is the force produced, measured in newtons
 indicates a vector cross product  is electric charge that the magnetic field is acting on, measured in coulombs  is velocity of the electric charge , measured in metres per second Because magnetic field is the relativistic product of Lorentz transformations, the force it produces is called the Lorentz force. The newton (symbol: N) is the SI unit of force. ...
In mathematics, the cross product is a binary operation on vectors in a three-dimensional Euclidean space. ...
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The coulomb (symbol: C) is the SI unit of electric charge. ...
The velocity of an object is simply its speed in a particular direction. ...
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Metre per second (U.S. spelling: meter per second) is an SI derived unit of both speed (scalar) and velocity (vector), defined by distance in metres divided by time in seconds. ...
A Lorentz transformation (LT) is a linear transformation that preserves the spacetime interval between any two events in Minkowski space, while leaving the origin fixed. ...
In physics, the Lorentz force is the force exerted on a charged particle in an electromagnetic field. ...
The force due to the magnetic field is different in different frames—moving magnetic field transforms partially or fully back into electric fields under Lorentz transformations. This results in Faraday induction law. A Lorentz transformation (LT) is a linear transformation that preserves the spacetime interval between any two events in Minkowski space, while leaving the origin fixed. ...
Magnetic field of flow (current) of charged particles Substituting into the definition of magnetic field  the proper electric field of point-like charge (see Coulomb's law) Proper in control theory Proper denotes a transfer function where the degree of the numerator does not exceed the degree of the denominator. ...
In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. ...
In physics, Coulombs law is an inverse-square law indicating the magnitude and direction of electrostatic force that one stationary, electrically charged object of small dimensions (ideally, a point source) exerts on another. ...
 results in the equation:  This equation is usually called Biot-Savart law. The Biot-Savart law is a physical law with applications in both electromagnetics and aerodynamics. ...
Here : is electric charge - motion of which creates the magnetic field - measured in coulombs ‹ The template below has been proposed for deletion. ...
- is velocity of the electric charge that is generating B, measured in metres per second
- B is the magnetic field (measured in teslas)
The velocity of an object is simply its speed in a particular direction. ...
‹ The template below has been proposed for deletion. ...
Metre per second (U.S. spelling: meter per second) is an SI derived unit of both speed (scalar) and velocity (vector), defined by distance in metres divided by time in seconds. ...
The tesla (symbol T) is the SI derived unit of magnetic flux density (or magnetic induction). ...
Lorentz force on wire segment The Lorentz force on a stationary wire carrying moving charges (=current) is therefore:  where - F = force (newton)
- B = flux density (tesla)
- L = length of wire (metre)
- i = current in wire (ampere)
In the equation above, the current vector i is a vector with magnitude equal to the scalar current, i, and direction pointing along the wire that the current is flowing. Alternatively, instead of current the wire segment can be considered a vector.
Vector calculus Separating electric field of moving charge into stationary electric and stationary magnetic components (= as measured by stationary observer)—which are usually labeled as E and B—replaces complex Einstein relativistic field transformation equations by more compact and elegant mathematical statements known as Maxwell equations. Two of them which describe magnetic component are: Maxwells equations are the set of four equations, attributed to James Clerk Maxwell, that describe the behavior of both the electric and magnetic fields, as well as their interactions with matter. ...
  where  is the curl operator  is the divergence operator  is permeability  is current density  is the partial derivative  is the free-space permittivity  is the electric field  is time The first equation is known as Ampère's law with James Clerk Maxwell's correction. The second term of this equation (Maxwell's correction) disappears in static (time independent) systems. The second equation is a statement of the observed non-existence of magnetic monopoles. These are two of four Maxwell's equations written in differential notation (introduced by Oliver Heaviside). This article is about the cURL command line tool. ...
In vector calculus, the divergence is an operator that measures a vector fields tendency to originate from or converge upon a given point. ...
In electromagnetism, permeability is the degree of magnetisation of a material that responds linearly to an applied magnetic field. ...
In electricity, current is the rate of flow of charges, usually through a metal wire or some other electrical conductor. ...
In mathematics, a partial derivative of a function of several variables is its derivative with respect to one of those variables with the others held constant. ...
Permittivity is a physical quantity that describes how an electric field affects and is affected by a medium. ...
In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. ...
A pocket watch. ...
André-Marie Ampère (January 22, 1775 – June 10, 1836), was a French physicist who is generally credited as one of the main discoverers of electromagnetism. ...
James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish mathematical physicist, born in Edinburgh. ...
In physics, a magnetic monopole is a hypothetical particle that may be loosely described as a magnet with only one pole (see electromagnetic theory for more on magnetic poles). ...
Maxwells equations (sometimes called the Maxwell equations) are the set of four equations, attributed to James Clerk Maxwell, that describe the behavior of both the electric and magnetic fields, as well as their interactions with matter. ...
Oliver Heaviside (May 18, 1850 – February 3, 1925) was a self-taught English engineer, mathematician and physicist who adapted complex numbers to the study of electrical circuits, developed techniques for applying Laplace transforms to the solution of differential equations, reformulated Maxwells field equations in terms of electric and magnetic...
Energy in the magnetic field If to divide the energy of a long (or toroidal) solenoid LI2 / 2 by the volume of the solenoid, the density of magnetic field energy can be obtained:  For example, magnetic field B = 1 tesla has energy density about 398 kilojoules per cubic meter, and of 10 teslas, about 40 megajoules per cubic meter.
The same is the pressure produced by magnetic field (pressure and energy density are essentially the same physical quantities and thus have the same units). Thus, magnetic field of 1 tesla produces pressure of 398 kPa (about 4 atmospheres), and 10 T about 40 Mpa (~400 atm).
Properties Maxwell did much to unify static electricity and magnetism, producing a set of four equations relating the two fields. However, under Maxwell's formulation, there were still two distinct fields describing different phenomena. It was Albert Einstein who showed, using special relativity, that electric and magnetic fields are two aspects of the same thing (a rank-2 tensor), and that one observer may perceive a magnetic force where a moving observer perceives only an electrostatic force. Thus, using special relativity, magnetic forces are a manifestation of electrostatic forces of charges in motion and may be predicted from knowledge of the electrostatic forces and the movement (relative to some observer) of the charges. Albert Einstein, photographed by Oren J. Turner in 1947. ...
Special relativity (SR) or the special theory of relativity is the physical theory published in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. It replaced Newtonian notions of space and time and incorporated electromagnetism as represented by Maxwells equations. ...
In mathematics, a tensor is a generalized quantity or a certain kind of geometrical entity that includes all the ideas of scalars, vectors, matrices and linear operators. ...
Electrostatics is the branch of physics that deals with the force exerted by a static (i. ...
Changing magnetic field is mathematically the same as moving magnetic field (see relativity of motion)—thus according to Einstein's field transformation equations (= Lorentz transformation of field from proper reference frame to non-moving reference frame) part of it appears as electric field component—this is known as Faraday's law of induction and is the principle behind electric generators and electric motors. In physics, the term relativity is used in several, related contexts: Galileo first developed the principle of relativity, which is the postulate that the laws of physics are the same for all observers. ...
Proper in control theory Proper denotes a transfer function where the degree of the numerator does not exceed the degree of the denominator. ...
Faradays law of induction gives the relation between the rate of change of the magnetic flux through the surface S enclosed by a contour C and the electric field induced along the contour: where E is the induced electric field, dl is an infinitesimal element of the contour C...
Generator redirects here. ...
Electric motors of various sizes. ...
Magnetic field lines The direction of magnetic field lines is defined as the direction of orientation of magnetic dipole—say, a small magnet or a loop of current in the magnetic field. Magnet from Practical Physics, publ. ...
Magnet from Practical Physics, publ. ...
This article is about the electromagnetic phenomenon. ...
Pole labeling confusions The "north" and "south" poles of a magnet or a magnetic dipole are labelled somewhat confusingly in comparison to the geographic north and south poles. In particular, the "north pole" of the Earth's magnetic dipole moment is located at the geographic (magnetic) south pole and vice versa. This article is about the electromagnetic phenomenon. ...
The North Pole is the northernmost point on the Earth. ...
Location of the South Pole in the Antarctic continent. ...
Earth is the third planet in the Solar system. ...
Location of the South Pole in the Antarctic continent. ...
By convention, the pole of a magnet is labelled according to the geographic direction it points in the presence of the Earth's magnetic field. Hence, when we speak of the "north pole" of a magnet, it is a reference to the "north-seeking" pole. Equivalently, magnetic field lines run from the north to the south pole of a magnet. (The geomagnetic field lines thus run from south to north along the Earth's surface.)
Rotating magnetic fields A rotating magnetic field is a magnetic field which rotates in polarity at non-relativistic speeds. This is a key principle to the operation of alternating-current motor. A permanent magnet in such a field will rotate so as to maintain its alignment with the external field. This effect is utilised in alternating current electric motors. Rotating magnetic field can be constructed using three or more phase alternating currents. Synchronous motors and induction motors use a stator's rotating magnetic fields to turn rotors. An alternator is an electromechanical device that converts mechanical energy to alternating current electrical energy. ...
Electric motors of various sizes. ...
shading-coils within the magnetic circuit of the field coil Shaded-pole synchronous motors are a class of AC motor. ...
Electric motors of various sizes. ...
The stator is the fixed part of a rotating machine. ...
R0t0r is from efnet ...
In 1882, Nikola Tesla identified the concept of the rotating magnetic field. In 1885, Galileo Ferraris independently researched the concept. In 1888, Tesla gained U.S. Patent 381968 for his work. Also in 1888, Ferraris published his research in a paper to the Royal Academy of Sciences in Turin. 1882 (MDCCCLXXXII) was a common year starting on Sunday (see link for calendar). ...
Nikola Tesla (July 10, 1856 - c. ...
1885 (MDCCCLXXXV) is a common year starting on Thursday. ...
Galileo Ferraris (October 30, 1847 - February 7, 1897) was an Italian physicist and electrical engineer, noted mostly for his studies on alternating current. ...
1888 (MDCCCLXXXVIII) is a leap year starting on Sunday (click on link for calendar) of the Gregorian calendar or a leap year starting on Tuesday of the Julian calendar. ...
Turin (Italian: ; Piedmontese: TürÃn) is a major industrial city in north-western Italy, capital of the Piedmont region, located mainly on the west bank of the Po River. ...
Hall effect Because Lorentz force is charge sign dependent (see above), it results in a charges separation, when a conductor with curent is placed in transverse magnetic field—with a buildup of opposite charges on two opposite sides of conductor (in the direction normal to the magnetic field direction)—and the potential difference between these sides can be measured. In physics, the Lorentz force is the force exerted on a charged particle in an electromagnetic field. ...
Hall effect is often used to measure the magnitude of magetic field.
See also General - Electric field - effect produced by an electric charge that exerts a force on charged objects in its vicinity.
- Electromagnetic field - a field composed of two related vector fields, the electric field and the magnetic field.
- Electromagnetism - the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field.
- Magnetism - phenomenon by which materials exert an attractive or repulsive force on other materials.
- Magnetohydrodynamics - the academic discipline which studies the dynamics of electrically conducting fluids.
Mathematics In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. ...
To meet Wikipedias quality standards, this article or section may require cleanup. ...
Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, which exerts a force on those particles that possess the property of electric charge, and is in turn affected by the presence and motion of such particles. ...
In physics, magnetism is one of the phenomena by which materials exert an attractive or repulsive force on other materials. ...
Magnetohydrodynamics (MHD) (magnetofluiddynamics or hydromagnetics), is the academic discipline which studies the dynamics of electrically conducting fluids. ...
- Ampere's law - magnetic equivalent of Gauss's law.
- Biot-Savart law - describes the magnetic field set up by a steadily flowing line current.
- Magnetic helicity - extent to which a magnetic field "wraps around itself".
- Maxwell's equations - four equations describing the behavior of the electric and magnetic fields, and their interaction with matter.
Applications In physics, Ampères law is the magnetic equivalent of Gausss law, discovered by André-Marie Ampère. ...
The Biot-Savart law is a physical law with applications in both electromagnetics and aerodynamics. ...
this page is about helicity in magnetic fields. ...
Maxwells equations (sometimes called the Maxwell equations) are the set of four equations, attributed to James Clerk Maxwell, that describe the behavior of both the electric and magnetic fields, as well as their interactions with matter. ...
- Helmholtz coil - a device for producing a region of nearly uniform magnetic field.
- Maxwell coil - a device for producing a large volume of almost constant magnetic field.
- Earth's magnetic field - a discussion of the magnetic field of the Earth.
- Dynamo theory - a proposed mechanism for the creation of the Earth's magnetic field.
- Electric motor - AC motors used magnetic fields
The term Helmholtz coils refers to a device for producing a region of nearly uniform magnetic field. ...
Maxwell coil layout in cylindrical coordinates. ...
This article or section does not cite its references or sources. ...
The Dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a magnetic field. ...
Electric motors of various sizes. ...
References Books - Griffiths, David J. (1998). Introduction to Electrodynamics (3rd ed.), Prentice Hall. ISBN 013805326X.
- Jackson, John D. (1998). Classical Electrodynamics (3rd ed.), Wiley. ISBN 047130932X.
- Tipler, Paul (2004). Physics for Scientists and Engineers: Electricity, Magnetism, Light, and Elementary Modern Physics (5th ed.), W. H. Freeman. ISBN 0716708108.
External articles Information Rotating magnetic fields July 17 is the 198th day (199th in leap years) of the year in the Gregorian calendar, with 167 days remaining. ...
2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ...
Diagrams - McCulloch, Malcolm,"A2: Electrical Power and Machines", Rotating magnetic field. eng.ox.ac.uk.
- "AC Motor Theory" Figure 2 Rotating Magnetic Field. Integrated Publishing.
Journal Articles - Yaakov Kraftmakher, "Two experiments with rotating magnetic field". 2001 Eur. J. Phys. 22 477-482.
- Bogdan Mielnik and David J. Fernández C., "An electron trapped in a rotating magnetic field". Journal of Mathematical Physics, February 1989, Volume 30, Issue 2, pp. 537-549.
- Sonia Melle, Miguel A. Rubio and Gerald G. Fuller "Structure and dynamics of magnetorheological fluids in rotating magnetic fields". Phys. Rev. E 61, 4111–4117 (2000).
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