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Magnetic pressure
 
 
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Magnetic pressure is an energy density
Energy density

Energy density is the amount of energy stored in a given system or region of space per unit volume, or per unit mass, depending on the context, although the latter is more formally specific energy ....
 associated with the magnetic field
Magnetic field

A magnetism field is a vector field which can exert a magnetic force on moving electric charges and on magnetic dipoles . When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field....
. It is identical to any other physical pressure
Pressure

Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
 except that it is carried by the magnetic field rather than (in the case of gas
Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
) kinetic energy
Kinetic energy

The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the mechanical work needed to accelerate a body of a given mass from rest to its current velocity....
 of the gas molecules. Interplay between magnetic pressure and ordinary gas pressure is important to both the fields of magnetohydrodynamics
Magnetohydrodynamics

Magnetohydrodynamics is the academic discipline which studies the dynamics of electrical conduction fluids. Examples of such fluids include Plasma , liquid metals, and Brine....
 and plasma physics. Any magnetic field has an associated pressure that is contained by the boundary conditions on the field, and a gradient in field strength causes a force due to the magnetic pressure gradient
Pressure gradient

In atmospheric sciences , the pressure gradient is a physical quantity that describes in which direction and at what rate the pressure changes the most rapidly around a particular location....
; this force is called the magnetic pressure force.

The magnetic pressure force is most readily observed in an unsupported loop of wire
Wire

A wire is a single, usually cylinder , elongated string of metal. Wires are used to bear mechanical Structural loads and to carry electricity and telecommunications Wiktionary:signal....
: if an electric current
Electric current

Electric current is the flow of electric charge. The electric charge may be either electrons or ions.The International System of Units unit of electric current intensity is the ampere....
 passes through the loop, then the wire serves as an electromagnet
Electromagnet

An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric Current . The magnetic field disappears when the current ceases....
, so that the magnetic field strength inside the loop is much greater than the field strength just outside the loop.






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Magnetic pressure is an energy density
Energy density

Energy density is the amount of energy stored in a given system or region of space per unit volume, or per unit mass, depending on the context, although the latter is more formally specific energy ....
 associated with the magnetic field
Magnetic field

A magnetism field is a vector field which can exert a magnetic force on moving electric charges and on magnetic dipoles . When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field....
. It is identical to any other physical pressure
Pressure

Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
 except that it is carried by the magnetic field rather than (in the case of gas
Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
) kinetic energy
Kinetic energy

The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the mechanical work needed to accelerate a body of a given mass from rest to its current velocity....
 of the gas molecules. Interplay between magnetic pressure and ordinary gas pressure is important to both the fields of magnetohydrodynamics
Magnetohydrodynamics

Magnetohydrodynamics is the academic discipline which studies the dynamics of electrical conduction fluids. Examples of such fluids include Plasma , liquid metals, and Brine....
 and plasma physics. Any magnetic field has an associated pressure that is contained by the boundary conditions on the field, and a gradient in field strength causes a force due to the magnetic pressure gradient
Pressure gradient

In atmospheric sciences , the pressure gradient is a physical quantity that describes in which direction and at what rate the pressure changes the most rapidly around a particular location....
; this force is called the magnetic pressure force.

The magnetic pressure force is most readily observed in an unsupported loop of wire
Wire

A wire is a single, usually cylinder , elongated string of metal. Wires are used to bear mechanical Structural loads and to carry electricity and telecommunications Wiktionary:signal....
: if an electric current
Electric current

Electric current is the flow of electric charge. The electric charge may be either electrons or ions.The International System of Units unit of electric current intensity is the ampere....
 passes through the loop, then the wire serves as an electromagnet
Electromagnet

An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric Current . The magnetic field disappears when the current ceases....
, so that the magnetic field strength inside the loop is much greater than the field strength just outside the loop. The gradient in field strength gives rise to a magnetic pressure force that tends to stretch the wire uniformly outward. If enough current travels through the wire, then the loop of wire will form a circle
Circle

A circle is a simple shape of Euclidean geometry consisting of those point in a plane which are the same distance from a given point called the center....
. At even higher currents, the magnetic pressure can create tensile stress that exceeds the tensile strength
Tensile strength

Tensile strength , or is the Stress at which a material breaks or permanently deforms. Tensile strength is an Intensive and extensive properties and, consequently, does not depend on the size of the test specimen....
 of the wire itself, causing it to fracture or even explosively fragment. Management of magnetic pressure is a significant challenge in the design of ultrastrong electromagnets. Magnetic pressure can be used to propel projectiles; this is the operating principle of a rail gun.

If any currents present are parallel to the field, the magnetic field lines follow shapes in which the magnetic pressure gradient is exactly balanced by the magnetic tension force
Magnetic tension force

The magnetic tension force is a Tension that exists along magnetic field lines. It is due to the existence of magnetic pressure and the linear nature of the magnetic field....
. Such a field configuration is called force-free
Force-free magnetic field

A force-free magnetic field is a type of field which arises as a special case from the magnetostatics equation in plasma . This special case arises when the plasma pressure is so small, relative to the magnetic pressure, that the plasma pressure may be ignored, and so only the magnetic pressure is considered....
, because there is no Lorentz force
Lorentz force

In physics, the Hendrik 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 field and magnetic fields:...
 . The familiar potential magnetic field is a special case of a force-free field: potential field configurations occupy space that contains no electric current
Electric current

Electric current is the flow of electric charge. The electric charge may be either electrons or ions.The International System of Units unit of electric current intensity is the ampere....
 at all.

The magnetic pressure is given in SI
International System of Units

The International System of Units is the modern form of the metric system and is generally a system devised around the convenience of the number ten....
 units (P in Pa
Pascal (unit)

The pascal is the SI derived unit of pressure, stress , Young's modulus and tensile strength. It is a measure of force per unit area i.e. equivalent to one newton per square meter or one joule per cubic meter....
, B in T
Tesla (unit)

The tesla is the SI derived unit of magnetic flux density B . The tesla is equal to one weber per square metre and was defined in 1960 in honor of inventor, scientist and electrical engineer Nikola Tesla....
, µ0 in H/m
Metre

The metre or meter is a Unit of measurement of length. It is the SI base unit of length in the metric system and in the International System of Units , used around the world for general and scientific purposes....
) by

and in cgs units (P in dyn/cm²
Barye

The barye , or sometimes barad, barrie, bary, baryd, baryed, or barie, was a Centimetre gram second system of units unit of pressure used in France....
, B in G
Gauss (unit)

The gauss, abbreviated as G, is the cgs units of measurement of a magnetic field B , named after the German mathematician and physicist Carl Friedrich Gauss....
) by

.

See also

  • Magnetic tension force
    Magnetic tension force

    The magnetic tension force is a Tension that exists along magnetic field lines. It is due to the existence of magnetic pressure and the linear nature of the magnetic field....