### Moses effect

In physics, Moses effect is a phenomenon of deformation of the surface of a diamagnetic liquid by a magnetic field. The effect was named after Biblical figure Moses, inspired by the crossing of the Red Sea in the Old Testament. The rapid progress in the development of neodymium magnets, supplying magnetic fields as high as ca. 1 T, allows simple and inexpensive experiments related to the Moses effect and its visualization. The application of magnetic fields on the order of magnitude of 0.5-1 T results in the formation of the near-surface “well” with a depth of dozens of micrometers. In contrast, the surface of a paramagnetic liquid is raised by the magnetic field.

### Loudspeaker

To make sound, a loudspeaker is driven by modulated electric current (produced by an amplifier) that passes through a "speaker coil" which then (through inductance) creates a magnetic field around the coil, creating a magnetic field. The electric current variations that pass through the speaker are thus converted to a varying magnetic field, whose interaction with the driver's magnetic field moves the speaker diaphragm, which thus forces the driver to produce air motion that is similar to the original signal from the amplifier.

### Maxwell coil

If the current in one of the coils is reversed, a uniform-gradient magnetic field is produced near the centre of the two coils. Maxwell describes the use of the 2-coil configuration for the generation of a uniform force on a small test coil. A Maxwell coil of this type is similar to a Helmholtz coil with the coil distance increased from coil radius R to \sqrt{3}R and the coils fed with opposite currents. Magnetic field. Halbach array.

### Electric potential

electrical potentialelectrostatic potentialCoulomb potential
When time-varying magnetic fields are present (which is true whenever there are time-varying electric fields and vice versa), it is not possible to describe the electric field simply in terms of a scalar potential V because the electric field is no longer conservative: is path-dependent because (Faraday's law of induction). Instead, one can still define a scalar potential by also including the magnetic vector potential A. In particular, A is defined to satisfy: where B is the magnetic field. Because the divergence of the magnetic field is always zero due to the absence of magnetic monopoles, such an A can always be found.

### Energy density

energy densitiesEnergies per unit massenergy
Electric and magnetic fields store energy. In a vacuum, the (volumetric) energy density is given by where E is the electric field and B is the magnetic field. The solution will be (in SI units) in Joules per cubic metre. In the context of magnetohydrodynamics, the physics of conductive fluids, the magnetic energy density behaves like an additional pressure that adds to the gas pressure of a plasma. In normal (linear and nondispersive) substances, the energy density (in SI units) is where D is the electric displacement field and H is the magnetizing field.

### Magnetic field viewing film

Magnetic filmfully coated
Magnetic field viewing film is used to show stationary or (less often) slowly changing magnetic fields; it shows their location and direction. It is a translucent thin flexible sheet, coated with micro-capsules containing nickel flakes suspended in oil. When magnetic lines of force are parallel to the surface of the carrier sheet, the surfaces of the flakes are reflective, and appear bright. When lines of force are perpendicular to the sheet, the flakes are edge-on, and appear significantly darker. When the film is placed on a magnet's pole, the latter case applies. Magnetic field viewing film together with a ruler can be used to measure the poles per inch of a magnet. Ferrofluid.

### Teltron tube

Teltron
In a uniform magnetic field however, charged particles follow a circular trajectory due to the cross product in the magnetic field term of the Lorentz force. (That is, the force from the magnetic field acts on the particle in a direction perpendicular to the particle's direction of motion. See: Lorentz force for more details.) The 'teltron' apparatus consists of a Teltron type electron deflection tube, a Teltron stand, EHT power supply (0 - 5000 V DC, variable). In an evacuated glass bulb some hydrogen gas (H 2 ) is filled, so that the tube has a hydrogen atmosphere at low pressure of about 1 Pa is formed.

### Potential energy

potentialpotential energiesgravitational potential
The energy of a magnetic moment in an externally produced magnetic B-field B has potential energy The magnetization M in a field is where the integral can be over all space or, equivalently, where M is nonzero. Magnetic potential energy is the form of energy related not only to the distance between magnetic materials, but also to the orientation, or alignment, of those materials within the field. For example, the needle of a compass has the lowest magnetic potential energy when it is aligned with the north and south poles of the Earth's magnetic field.

### Charge density

charge distributionelectric charge densitysurface charge density
Anthony French has described how the magnetic field force of a current-bearing wire arises from this relative charge density. He used (p 260) a Minkowski diagram to show "how a neutral current-bearing wire appears to carry a net charge density as observed in a moving frame." When a charge density is measured in a moving frame of reference it is called proper charge density. It turns out the charge density ρ and current density J transform together as a four current vector under Lorentz transformations.

### Einstein–de Haas effect

Einstein-de Haas effect
A change in magnetization, implies a proportional change in the angular momentum, of the electrons involved. Provided that there is no external torque along the magnetization axis applied to the body in the process, the rest of the body (practically all its mass) should acquire an angular momentum due to the law of conservation of angular momentum. The experiments involve a cylinder of a ferromagnetic material suspended with the aid of a thin string inside a cylindrical coil which is used to provide an axial magnetic field that magnetizes the cylinder along its axis.

### Kilogram

kgmgmilligram
Three other base units (cd, A, mol) and 17 derived units (N, Pa, J, W, C, V, F, Ω, S, Wb, T, H, kat, Gy, Sv, lm, lx) in the SI system were defined in relation to the kilogram, and thus its stability was important. The definitions of only eight other named SI units did not depend on the kilogram: those of temperature (K, °C), time and frequency (s, Hz, Bq), length (m), and angle (rad, sr). After the International Prototype Kilogram had been found to vary in mass over time relative to its reproductions, the International Committee for Weights and Measures (CIPM) recommended in 2005 that the kilogram be redefined in terms of a fundamental constant of nature.

### Earth's outer core

outer corecoreEarth's core
The Dynamo theory sees eddy currents in the nickel–iron fluid of the outer core as principal source of the Earth's magnetic field. The average magnetic field strength in the Earth's outer core was estimated to be 2.5 millitesla, 50 times stronger than the magnetic field at the surface. The outer core is not under enough pressure to be solid, so it is liquid even though it has a composition similar to the inner core. Sulfur and oxygen could be present in the outer core. As heat is transferred outward toward the mantle, the net trend is for the inner boundary of the liquid region to freeze, causing the solid inner core to grow at expense of the outer core.

### Convection

convectiveconvection currentsconvection current
Thermomagnetic convection can occur when an external magnetic field is imposed on a ferrofluid with varying magnetic susceptibility. In the presence of a temperature gradient this results in a nonuniform magnetic body force, which leads to fluid movement. A ferrofluid is a liquid which becomes strongly magnetized in the presence of a magnetic field. This form of heat transfer can be useful for cases where conventional convection fails to provide adequate heat transfer, e.g., in miniature microscale devices or under reduced gravity conditions. Capillary action is a phenomenon where liquid spontaneously rises in a narrow space such as a thin tube, or in porous materials.

### Upward continuation

Upward continuation is a method used in oil exploration and geophysics to estimate the values of a gravitational or magnetic field by using measurements at a lower elevation and extrapolating upward, assuming continuity. This technique is commonly used to merge different measurements to a common level so as to reduce scatter and allow for easier analysis. *Petroleum geology Upward Continuation in Schlumberger's Oilfield Glossary. Downward Continuation in Schlumberger's Oilfield Glossary.

### Newton (unit)

kNnewtonN
The newton (symbol: N) is the International System of Units (SI) derived unit of force. It is named after Isaac Newton in recognition of his work on classical mechanics, specifically Newton's second law of motion.

### Elementary particle

elementary particlesparticleparticles
In particle physics, an elementary particle or fundamental particle is a subatomic particle with no sub structure, thus not composed of other particles. Particles currently thought to be elementary include the fundamental fermions (quarks, leptons, antiquarks, and antileptons), which generally are "matter particles" and "antimatter particles", as well as the fundamental bosons (gauge bosons and the Higgs boson), which generally are "force particles" that mediate interactions among fermions. A particle containing two or more elementary particles is a composite particle.

### Quantum mechanics

quantum physicsquantum mechanicalquantum theory
Important applications of quantum theory include quantum chemistry, quantum optics, quantum computing, superconducting magnets, light-emitting diodes, the optical amplifier and the laser, the transistor and semiconductors such as the microprocessor, medical and research imaging such as magnetic resonance imaging and electron microscopy. Explanations for many biological and physical phenomena are rooted in the nature of the chemical bond, most notably the macro-molecule DNA. Many modern electronic devices are designed using quantum mechanics. Examples include the laser, the transistor (and thus the microchip), the electron microscope, and magnetic resonance imaging (MRI).

### Electrical engineering

electrical engineerelectricalElectrical and Electronics Engineering
Notable developments in this century include the work of Hans Christian Ørsted who discovered in 1820 that an electric current produces a magnetic field that will deflect a compass needle, of William Sturgeon who, in 1825 invented the electromagnet, of Joseph Henry and Edward Davy who invented the electrical relay in 1835, of Georg Ohm, who in 1827 quantified the relationship between the electric current and potential difference in a conductor, of Michael Faraday (the discoverer of electromagnetic induction in 1831), and of James Clerk Maxwell, who in 1873 published a unified theory of electricity and magnetism in his treatise Electricity and Magnetism.

### Electromechanics

electromechanicalelectro-mechanicalElectromechanical Engineering
The motor was developed only a year after Hans Christian Ørsted discovered that the flow of electric current creates a proportional magnetic field. This early motor was simply a wire partially submerged into a glass of mercury with a magnet at the bottom. When the wire was connected to a battery a magnetic field was created and this interaction with the magnetic field given off by the magnet caused the wire to spin. Ten years later the first electric generator was invented, again by Michael Faraday. This generator consisted of a magnet passing through a coil of wire and inducing current that was measured by a galvanometer.

That is, upon taking an initial bearing, one proceeds along the same bearing, without changing the direction as measured relative to true or magnetic north. Most modern navigation relies primarily on positions determined electronically by receivers collecting information from satellites. Most other modern techniques rely on crossing lines of position or LOP. A line of position can refer to two different things, either a line on a chart or a line between the observer and an object in real life. A bearing is a measure of the direction to an object.

### Petrus Peregrinus de Maricourt

Pierre de MaricourtPeter of MaricourtPetrus Peregrinus
He also treats the attraction of iron by lodestones, the magnetization of iron by lodestones, and the ability to reverse the polarity in such an induced magnet. Peregrinus attributed the Earth's magnetism to the action of celestial poles, rather than to the terrestrial poles of the planet itself. Part Two (three chapters): This section describes three devices that utilize the properties of magnets. He treats the practical applications of magnets, describing the “wet” floating compass as an instrument in common use, and proposing a new “dry” pivoted compass in some detail.

### William Gilbert (physician)

William GilbertGilbert, WilliamWilliam Gilbert (astronomer)
His primary scientific work—much inspired by earlier works of Robert Norman —was De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (On the Magnet and Magnetic Bodies, and on the Great Magnet the Earth) published in 1600. In this work, he describes many of his experiments with his model Earth called the terrella. From these experiments, he concluded that the Earth was itself magnetic and that this was the reason compasses point north (previously, some believed that it was the pole star (Polaris) or a large magnetic island on the north pole that attracted the compass).

### Colchester

Colchester, EssexColchester, EnglandColchester Town Hall
William Gilbert (1544–1603) – scientist, pioneer in the field of magnetism and court physician to Elizabeth I and James I. William Gull (1816–1890) – Physician-in-Ordinary to Queen Victoria; Governor of Guy's Hospital; researched and named anorexia nervosa. William Hale (1797–1870) – early rocket engineer. Samuel Harsnett (1561–1631) – writer and Archbishop of York. Klaus Kinski (1926–1991) – actor, director, former German POW in Colchester during the World War II. Charles Lucas (1613–1648) – Royalist soldier in the English Civil War and Siege of Colchester. Alfred Lungley (1905–1989) – awarded the George Cross after the Quetta earthquake of 1935.

### De Magnete

De Magnete, Magneticisque Corporibus, et de Magno Magnete TellureOn the Loadstone and Magnetic BodiesDe magnete, magneticisque corporibus
De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (On the Magnet and Magnetic Bodies, and on That Great Magnet the Earth) is a scientific work published in 1600 by the English physician and scientist William Gilbert and his partner Aaron Dowling. A highly influential and successful book, it exerted an immediate influence on many contemporary writers, including Francis Godwin and Mark Ridley. In his work, Gilbert described many of his experiments with his model Earth called the terrella. (Previously, it was thought that Polaris or a large magnetic island at the North Pole attracted the compass).

### John Michell

Michell, John
Michell studied magnetism and discovered the "inverse-square law", the fact that the magnetic force exerted by each pole of a magnet decreases in proportion to the square of the distance between them. His 1750 paper Treatise of Artificial Magnets, which was written for seamen and instrument makers and intended as a practical manual on how to make magnets, included a list of the "Properties of Magnetical Bodies" that represented a major contribution to the understanding of magnetism. Michell devised a torsion balance for measuring the mass of the Earth, but died before he could use it.