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Related Concept Videos

Magnetostatic Boundary Conditions01:28

Magnetostatic Boundary Conditions

An electric field suffers a discontinuity at a surface charge. Similarly, a magnetic field is discontinuous at a surface current. The perpendicular component of a magnetic field is continuous across the interface of two magnetic mediums. In contrast, its parallel component, perpendicular to the current, is discontinuous by the amount equal to the product of the vacuum permeability and the surface current. Like the scalar potential in electrostatics, the vector potential is also continuous...
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The magnetic field due to a volume current distribution given by the Biot–Savart Law can be expressed as follows:
Magnetic Fields01:27

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A moving charge or a current creates a magnetic field in the surrounding space, in addition to its electric field. The magnetic field exerts a force on any other moving charge or current that is present in the field. Like an electric field, the magnetic field is also a vector field. At any position, the direction of the magnetic field is defined as the direction in which the north pole of a compass needle points.
A magnetic field is defined by the force that a charged particle experiences...
Magnetic Field due to Moving Charges01:23

Magnetic Field due to Moving Charges

A stationary charge creates and interacts with the electric field, while a moving charge creates a magnetic field.
Consider a point charge moving with a constant velocity. Like the electric field, the magnetic field at any point is directly proportional to the magnitude of the charge and inversely proportional to the square of the distance between the source point and the field point. However, unlike the electric field, the magnetic field is always perpendicular to the plane containing the line...
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The most common application of magnetic force on current-carrying wires is in electric motors. These consist of loops of wire, which are placed between the magnets with a magnetic field. When current flows through the loops, the magnetic field applies torque, which causes the shaft to rotate, thus converting electrical energy to mechanical energy.
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Magnetic Flux

The magnetic flux measures the number of magnetic field lines passing through a given surface area. The SI unit for magnetic flux is the weber (Wb). Magnetic flux is a scalar quantity. It depends on three factors: the strength of the magnetic field B, the area through which the field lines pass, and the relative orientation of the field with the surface area.
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Updated: Jun 14, 2026

Magnetically Induced Rotating Rayleigh-Taylor Instability
06:42

Magnetically Induced Rotating Rayleigh-Taylor Instability

Published on: March 3, 2017

Turbulent magnetic diffusivity tensor for time-dependent mean fields.

David W Hughes1, Michael R E Proctor

  • 1Institut Henri Poincaré, 11 rue Pierre et Marie Curie, 75005 Paris, France. d.w.hughes@leeds.ac.uk

Physical Review Letters
|April 7, 2010
PubMed
Summary
This summary is machine-generated.

This study corrects the calculation of turbulent magnetic diffusivity in mean field electrodynamics. It shows that including time derivatives of the mean magnetic field is crucial for accurate growth rate predictions.

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Area of Science:

  • Plasma physics
  • Astrophysical fluid dynamics
  • Magnetohydrodynamics

Background:

  • Mean field electrodynamics is essential for understanding cosmic magnetic fields.
  • The turbulent magnetic diffusivity tensor is a key component in these models.
  • Previous calculations often assume time-independent mean magnetic fields.

Purpose of the Study:

  • To reexamine the turbulent magnetic diffusivity tensor in mean field electrodynamics.
  • To identify inaccuracies in predicted mean field growth rates.
  • To propose an extended calculation method for the mean electromotive force.

Main Methods:

  • Revisiting the theoretical framework of mean field electrodynamics.
  • Extending the traditional expansion procedure for the mean electromotive force.
  • Employing perturbation analysis for mean magnetic fields with long spatial scales.

Main Results:

  • The predicted growth rate of the mean field is generally incorrect when using time-independent mean magnetic fields.
  • An extended expansion procedure including time derivatives of the mean magnetic field is necessary.
  • The magnitude of the new magnetic diffusion contribution was examined for a specific flow.

Conclusions:

  • The standard calculation of the turbulent magnetic diffusivity tensor requires refinement.
  • Incorporating time derivatives of the mean magnetic field improves the accuracy of mean field electrodynamics.
  • This revised approach offers a more consistent description of magnetic field generation and evolution.