Magnetic tension forces also rely on vector current densities and their interaction with the magnetic field. Plotting magnetic tension along adjacent field lines can give a picture as to their divergence and convergence with respect to each other as well as current densities.[citation needed]
Magnetic tension is analogous to the restoring force of rubber bands.[1]
where the first term on the right hand side represents the Lorentz force and the second term represents pressure gradient forces. The Lorentz force can be expanded using Ampère's law, , and the vector identity
to give
where the first term on the right hand side is the magnetic tension and the second term is the magnetic pressure force.
The force due to changes in the magnitude of and its direction can be separated by writing with and a unit vector:
where the spatial constancy of the magnitude has been assumed and
has magnitude equal to the curvature, or the reciprocal of the radius of curvature, and is directed from a point on a magnetic field line to the center of curvature. Therefore, as the curvature of the magnetic field line increases, so too does the magnetic tension force resisting this curvature.[2][1]
Magnetic tension and pressure are both implicitly included in the Maxwell stress tensor. Terms representing these two forces are present along the main diagonal where they act on differential area elements normal to the corresponding axis.
Plasma physicsedit
Magnetic tension is particularly important in plasma physics and MHD, where it controls dynamics of some systems and the shape of magnetic structures. For example, in a homogeneous magnetic field and an absence of gravity, magnetic tension is the sole driver of linear Alfvén waves.[3]
^ abHood, Alan. "The Lorentz Force - Magnetic Pressure and Tension". www-solar.mcs.st-andrews.ac.uk. Retrieved 14 May 2022.
^Bellan, Paul Murray (2006). Fundamentals of Plasma Physics. Cambridge: Cambridge University Press. pp. 268–272. ISBN9780511807183.
^Vial, Jean-Claude; Engvold, Oddbjørn (2015). Solar Prominences. Springer. ISBN978-3-319-10415-7.
January 01, 1970
magnetic, tension, physics, magnetic, tension, restoring, force, with, units, force, density, that, acts, straighten, bent, magnetic, field, lines, units, force, density, displaystyle, mathbf, exerted, perpendicular, magnetic, field, displaystyle, mathbf, expr. In physics magnetic tension is a restoring force with units of force density that acts to straighten bent magnetic field lines In SI units the force density f T displaystyle mathbf f T exerted perpendicular to a magnetic field B displaystyle mathbf B can be expressed asThe magnetic tension force depicted by the red arrow acts to straighten the bent magnetic field lines in black f T B B m 0 displaystyle mathbf f T frac left mathbf B cdot nabla right mathbf B mu 0 where m 0 displaystyle mu 0 is the vacuum permeability Magnetic tension forces also rely on vector current densities and their interaction with the magnetic field Plotting magnetic tension along adjacent field lines can give a picture as to their divergence and convergence with respect to each other as well as current densities citation needed Magnetic tension is analogous to the restoring force of rubber bands 1 Contents 1 Mathematical statement 2 Plasma physics 3 See also 4 ReferencesMathematical statement editIn ideal magnetohydrodynamics MHD the magnetic tension force in an electrically conducting fluid with a bulk plasma velocity field v displaystyle mathbf v nbsp current density J displaystyle mathbf J nbsp mass density r displaystyle rho nbsp magnetic field B displaystyle mathbf B nbsp and plasma pressure p displaystyle p nbsp can be derived from the Cauchy momentum equation r t v v J B p displaystyle rho left frac partial partial t mathbf v cdot nabla right mathbf v mathbf J times mathbf B nabla p nbsp where the first term on the right hand side represents the Lorentz force and the second term represents pressure gradient forces The Lorentz force can be expanded using Ampere s law m 0 J B displaystyle mu 0 mathbf J nabla times mathbf B nbsp and the vector identity 1 2 B B B B B B displaystyle tfrac 1 2 nabla mathbf B cdot mathbf B mathbf B cdot nabla mathbf B mathbf B times nabla times mathbf B nbsp to give J B B B m 0 B 2 2 m 0 displaystyle mathbf J times mathbf B mathbf B cdot nabla mathbf B over mu 0 nabla left frac B 2 2 mu 0 right nbsp where the first term on the right hand side is the magnetic tension and the second term is the magnetic pressure force The force due to changes in the magnitude of B displaystyle mathbf B nbsp and its direction can be separated by writing B B b displaystyle mathbf B B mathbf b nbsp with B B displaystyle B mathbf B nbsp and b displaystyle mathbf b nbsp a unit vector B B m 0 B 2 m 0 b b B 2 m 0 k displaystyle mathbf B cdot nabla mathbf B over mu 0 frac B 2 mu 0 mathbf b cdot nabla mathbf b frac B 2 mu 0 boldsymbol kappa nbsp where the spatial constancy of the magnitude has been assumed B 0 displaystyle nabla B 0 nbsp and k b b displaystyle boldsymbol kappa mathbf b cdot nabla mathbf b nbsp has magnitude equal to the curvature or the reciprocal of the radius of curvature and is directed from a point on a magnetic field line to the center of curvature Therefore as the curvature of the magnetic field line increases so too does the magnetic tension force resisting this curvature 2 1 Magnetic tension and pressure are both implicitly included in the Maxwell stress tensor Terms representing these two forces are present along the main diagonal where they act on differential area elements normal to the corresponding axis Plasma physics editMagnetic tension is particularly important in plasma physics and MHD where it controls dynamics of some systems and the shape of magnetic structures For example in a homogeneous magnetic field and an absence of gravity magnetic tension is the sole driver of linear Alfven waves 3 See also editMagnetic pinch Magnetosonic waveReferences edit a b Hood Alan The Lorentz Force Magnetic Pressure and Tension www solar mcs st andrews ac uk Retrieved 14 May 2022 Bellan Paul Murray 2006 Fundamentals of Plasma Physics Cambridge Cambridge University Press pp 268 272 ISBN 9780511807183 Vial Jean Claude Engvold Oddbjorn 2015 Solar Prominences Springer ISBN 978 3 319 10415 7 Retrieved from https en wikipedia org w index php title Magnetic tension amp oldid 1187098306, wikipedia, wiki, book, books, library,