Magnetic field

The shape of the magnetic field produced by a horseshoe magnet is revealed by the orientation of iron filings sprinkled on a piece of paper above the magnet.
Right hand grip rule: a current flowing in the direction of the white arrow produces a magnetic field shown by the red arrows.
A Solenoid with electric current running through it behaves like a magnet.
A sketch of Earth's magnetic field representing the source of the field as a magnet. The south pole of the magnetic field is near the geographic north pole of the Earth.
One of the first drawings of a magnetic field, by René Descartes, 1644, showing the Earth attracting lodestones. It illustrated his theory that magnetism was caused by the circulation of tiny helical particles, "threaded parts", through threaded pores in magnets.
Hans Christian Ørsted, Der Geist in der Natur, 1854

Vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials.

- Magnetic field
The shape of the magnetic field produced by a horseshoe magnet is revealed by the orientation of iron filings sprinkled on a piece of paper above the magnet.

101 related topics

Alpha

Eddy currents ( I, red ) induced in a conductive metal plate (C) as it moves to the right under a magnet (N). The magnetic field ( B, green ) is directed down through the plate. The Lorentz force of the magnetic field on the electrons in the metal induces a sideways current under the magnet.  The magnetic field, acting on the sideways moving electrons, creates a Lorentz force opposite to the velocity of the sheet, which acts as a drag force on the sheet.  The blue arrows are counter magnetic fields generated by the circular motion of the charges.

Eddy current

Eddy currents ( I, red ) induced in a conductive metal plate (C) as it moves to the right under a magnet (N). The magnetic field ( B, green ) is directed down through the plate. The Lorentz force of the magnetic field on the electrons in the metal induces a sideways current under the magnet.  The magnetic field, acting on the sideways moving electrons, creates a Lorentz force opposite to the velocity of the sheet, which acts as a drag force on the sheet.  The blue arrows are counter magnetic fields generated by the circular motion of the charges.
(left) Eddy currents ( I, red ) within a solid iron transformer core. (right) Making the core out of thin laminations parallel to the field ( B, green ) with insulation (C) between them reduces the eddy currents. Although the field and currents are shown in one direction, they actually reverse direction with the alternating current in the transformer winding.
A cross section through a linear motor placed above a thick aluminium slab. As the linear induction motor's field pattern sweeps to the left, eddy currents are left behind in the metal and this causes the field lines to lean.
Lamination of magnetic cores in transformers greatly improves the efficiency by minimising eddy currents
E-I transformer laminations showing flux paths. The effect of the gap where the laminations are butted together can be mitigated by alternating pairs of E laminations with pairs of I laminations, providing a path for the magnetic flux around the gap.
Eddy current brake. The North magnetic pole piece (top) in this drawing is shown further away from the disk than the South; this is just to leave room to show the currents. In an actual eddy current brake the pole pieces are positioned as close to the disk as possible.

Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction.

Magnetisation curve for ferromagnets (and ferrimagnets) and corresponding permeability

Permeability (electromagnetism)

Magnetisation curve for ferromagnets (and ferrimagnets) and corresponding permeability

In electromagnetism, permeability is the measure of magnetization that a material obtains in response to an applied magnetic field.

Illustration of the electric field surrounding a positive (red) and a negative (blue) charge.

Field (physics)

Physical quantity, represented by a scalar, vector, or tensor, that has a value for each point in space and time.

Physical quantity, represented by a scalar, vector, or tensor, that has a value for each point in space and time.

Illustration of the electric field surrounding a positive (red) and a negative (blue) charge.
In classical gravitation, mass is the source of an attractive gravitational field g.
The E fields and B fields due to electric charges (black/white) and magnetic poles (red/blue). Top: E field due to an electric dipole moment d. Bottom left: B field due to a mathematical magnetic dipole m formed by two magnetic monopoles. Bottom right: B field due to a pure magnetic dipole moment m found in ordinary matter (not from monopoles).
The E fields and B fields due to electric charges (black/white) and magnetic poles (red/blue). E fields due to stationary electric charges and B fields due to stationary magnetic charges (note in nature N and S monopoles do not exist). In motion (velocity v), an electric charge induces a B field while a magnetic charge (not found in nature) would induce an E field. Conventional current is used.
In general relativity, mass-energy warps space time (Einstein tensor G), and rotating asymmetric mass-energy distributions with angular momentum J generate GEM fields H
Fields due to color charges, like in quarks (G is the gluon field strength tensor). These are "colorless" combinations. Top: Color charge has "ternary neutral states" as well as binary neutrality (analogous to electric charge). Bottom: The quark/antiquark combinations.

However, it became much more natural to take the field approach and express these laws in terms of electric and magnetic fields; in 1849 Michael Faraday became the first to coin the term "field".

James Clerk Maxwell

James Clerk Maxwell

Scottish mathematician and scientist responsible for the classical theory of electromagnetic radiation, which was the first theory to describe electricity, magnetism and light as different manifestations of the same phenomenon.

Scottish mathematician and scientist responsible for the classical theory of electromagnetic radiation, which was the first theory to describe electricity, magnetism and light as different manifestations of the same phenomenon.

James Clerk Maxwell
Clerk Maxwell's birthplace at 14 India Street in Edinburgh is now the home of the James Clerk Maxwell Foundation.
Edinburgh Academy, where Maxwell was educated
Old College, University of Edinburgh
A young Maxwell at Trinity College, Cambridge, holding one of his colour wheels.
Maxwell proved that the Rings of Saturn were made of numerous small particles.
James Clark Maxwell and his wife by Jemima Blackburn.
Commemoration of Maxwell's equations at King's College. One of three identical IEEE Milestone Plaques, the others being at Maxwell's birthplace in Edinburgh and the family home at Glenlair.
Blue plaque, 16 Palace Gardens Terrace, Kensington, Maxwell's home, 1860–1865
The gravestone at Parton Kirk (Galloway) of James Clerk Maxwell, his parents and his wife
This memorial stone to James Clerk Maxwell stands on a green in front of the church, beside the war memorial at Parton (Galloway).
James Clark Maxwell by Jemima Blackburn.
A postcard from Maxwell to Peter Tait
First durable colour photographic image, demonstrated by Maxwell in an 1861 lecture
Maxwell's demon, a thought experiment where entropy decreases
The James Clerk Maxwell Monument in Edinburgh, by Alexander Stoddart. Commissioned by The Royal Society of Edinburgh; unveiled in 2008.

With the publication of "A Dynamical Theory of the Electromagnetic Field" in 1865, Maxwell demonstrated that electric and magnetic fields travel through space as waves moving at the speed of light.

Depiction of a two-dimensional vector field with a uniform curl.

Curl (mathematics)

Vector operator that describes the infinitesimal circulation of a vector field in three-dimensional Euclidean space.

Vector operator that describes the infinitesimal circulation of a vector field in three-dimensional Euclidean space.

Depiction of a two-dimensional vector field with a uniform curl.

. This is why the magnetic field, characterized by zero divergence, can be expressed as the curl of a magnetic vector potential.

Pyrolytic carbon has one of the largest diamagnetic constants of any room temperature material. Here a pyrolytic carbon sheet is levitated by its repulsion from the strong magnetic field of neodymium magnets.

Diamagnetism

Pyrolytic carbon has one of the largest diamagnetic constants of any room temperature material. Here a pyrolytic carbon sheet is levitated by its repulsion from the strong magnetic field of neodymium magnets.
Diamagnetic material interaction in magnetic field.
Transition from ordinary conductivity (left) to superconductivity (right). At the transition, the superconductor expels the magnetic field and then acts as a perfect diamagnet.
A live frog levitates inside a 32 mm diameter vertical bore of a Bitter solenoid in a magnetic field of about 16 teslas at the Nijmegen High Field Magnet Laboratory.

Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force.

Lorentz force law

Hall effect

[[File:Hall effect.png|thumb|Hall-effect:

[[File:Hall effect.png|thumb|Hall-effect:

Lorentz force law
Hall effect current sensor with internal integrated circuit amplifier. 8 mm opening. Zero current output voltage is midway between the supply voltages that maintain a 4 to 8 volt differential. Non-zero current response is proportional to the voltage supplied and is linear to 60 amperes for this particular (25 A) device.
Diagram of Hall effect current transducer integrated into ferrite ring.
Multiple 'turns' and corresponding transfer function.
Corbino disc – dashed curves represent logarithmic spiral paths of deflected electrons

The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor that is transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current.

Momentum of a pool cue ball is transferred to the racked balls after collision.

Momentum

Product of the mass and velocity of an object.

Product of the mass and velocity of an object.

Momentum of a pool cue ball is transferred to the racked balls after collision.
Elastic collision of equal masses
Elastic collision of unequal masses
a perfectly inelastic collision between equal masses
Two-dimensional elastic collision. There is no motion perpendicular to the image, so only two components are needed to represent the velocities and momenta. The two blue vectors represent velocities after the collision and add vectorially to get the initial (red) velocity.
Motion of a material body

and magnetic field

Portrait by Napoleon Sarony, 1890s

Nikola Tesla

Serbian-American inventor, electrical engineer, mechanical engineer, and futurist best known for his contributions to the design of the modern alternating current (AC) electricity supply system.

Serbian-American inventor, electrical engineer, mechanical engineer, and futurist best known for his contributions to the design of the modern alternating current (AC) electricity supply system.

Portrait by Napoleon Sarony, 1890s
Rebuilt, Tesla's house (parish hall) in Smiljan, now in Croatia, region of Lika, where he was born, and the rebuilt church, where his father served. During the Yugoslav Wars, several of the buildings were severely damaged by fire. They were restored and reopened in 2006.
Tesla's baptismal record, 28 June 1856
Tesla's father, Milutin, was an Orthodox priest in the village of Smiljan.
Tesla aged 23, c. 1879
Edison Machine Works on Goerck Street, New York. Tesla found the change from cosmopolitan Europe to working at this shop, located amongst the tenements on Manhattan's lower east side, a "painful surprise".
Drawing from, illustrating the principle of Tesla's alternating current induction motor
Tesla's AC dynamo-electric machine (AC electric generator) in an 1888
Mark Twain in Tesla's South Fifth Avenue laboratory, 1894
Tesla demonstrating wireless lighting by "electrostatic induction" during an 1891 lecture at Columbia College via two long Geissler tubes (similar to neon tubes) in his hands
X-ray Tesla took of his hand
In 1898, Tesla demonstrated a radio-controlled boat which he hoped to sell as a guided torpedo to navies around the world.
Tesla sitting in front of a spiral coil used in his wireless power experiments at his East Houston St. laboratory
Tesla's Colorado Springs laboratory
A multiple exposure picture of Tesla sitting next to his "magnifying transmitter" generating millions of volts. The 7 m long arcs were not part of the normal operation, but only produced for effect by rapidly cycling the power switch.
Tesla's Wardenclyffe plant on Long Island in 1904. From this facility, Tesla hoped to demonstrate wireless transmission of electrical energy across the Atlantic.
Tesla's bladeless turbine design
Second banquet meeting of the Institute of Radio Engineers, 23 April 1915. Tesla is seen standing in the center.
Tesla on Time magazine commemorating his 75th birthday
Newspaper representation of the thought camera Tesla described at his 1933 birthday party
Room 3327 of the Hotel New Yorker, where Tesla died
Gilded urn with Tesla's ashes, in his favorite geometric object, a sphere (Nikola Tesla Museum, Belgrade)
Tesla c. 1896
Tesla c. undefined 1885
Nikola Tesla Museum in Belgrade, Serbia
Belgrade Nikola Tesla Airport was named after the scientist in 2006.
This Nikola Tesla statue in Zagreb, Croatia was made by Ivan Meštrović in 1954. It was located at the Ruđer Bošković Institute before it was moved to the Tesla street in the city center in 2006.
Nikola Tesla Corner in New York City
Nikola Tesla statue in Niagara Falls, Ontario

Tesla's work fell into relative obscurity following his death, until 1960, when the General Conference on Weights and Measures named the SI unit of magnetic flux density the tesla in his honor.

Vector arrow pointing from A to B

Euclidean vector

Geometric object that has magnitude (or length) and direction.

Geometric object that has magnitude (or length) and direction.

Vector arrow pointing from A to B
Illustration of tangential and normal components of a vector to a surface.
The subtraction of two vectors a and b
Scalar multiplication of a vector by a factor of 3 stretches the vector out.
The scalar multiplications −a and 2a of a vector a
The normalization of a vector a into a unit vector â

Other physical vectors, such as the electric and magnetic field, are represented as a system of vectors at each point of a physical space; that is, a vector field.