Journal Of Magnetic Resonance

journalJournal Of Magnetic Resonance
 
The Earth has a substantial magnetic field, a fact of some historical importance because of the role of the magnetic compass in exploration of the planet. Then, mark each location with an arrow (called a vector ) pointing in the direction of the local magnetic field with its magnitude proportional to the strength of the magnetic field. The direction of the magnetic field at any point is parallel to the direction of nearby field lines, and the local density of field lines can be made proportional to its strength. Magnetic field lines are like streamlines in fluid flow , in that they represent something continuous, and a different resolution would show more or fewer lines.Recent developments in the controlled movement of domain walls in magnetic nanowires by short pulses of spin-polarized current give promise of a nonvolatile memory device with the high performance and reliability of conventional solid-state memory but at the low cost of conventional magnetic disk drive storage.  An advantage of using magnetic field lines as a representation is that many laws of magnetism (and electromagnetism) can be stated completely and concisely using simple concepts such as the `number` of field lines through a surface. For example, the number of field lines through a given surface is the surface integral of the magnetic field. The direction of magnetic field lines represented by the alignment of iron filings sprinkled on paper placed above a bar magnet. The magnetic field of permanent magnets can be quite complicated, especially near the magnet.Just like plastic cards, the wood-based cards bend, and can be embedded with magnetic stripes or barcodes. The magnetic field of a small nb 8 straight magnet is proportional to the magnet`s strength (called its magnetic dipole moment m). The equations are non-trivial and also depend on the distance from the magnet and the orientation of the magnet. The magnetic field of larger magnets can be obtained by modelling them as a collection of a large number of small magnets called dipoles each having their own m. The magnetic field produced by the magnet then is the net magnetic field of these dipoles. And, any net force on the magnet is a result of adding up the forces on the individual dipoles.Blend Inbound Customer Contacts over any channel, with data driven routing to optimise your customer experience. These two models produce two different magnetic fields, H and B. Outside a material, though, the two are identical (to a multiplicative constant) so that in many cases the distinction can be ignored. This is particularly true for magnetic fields, such as those due to electric currents, that are not generated by magnetic materials. The magnetic pole model: two opposing poles, North (+) and South (−), separated by a distance d produce an H-field (lines). This is called the Gilbert model of magnetism, after William Gilbert In this model, a magnetic H-field is produced by magnetic charges that are `smeared` around each pole.Magnetic: Cage Closed is a first person puzzle game where the player manipulates magnetic forces to accomplish their goals.  It is sometimes useful to model the force and torques between two magnets as due to magnetic poles repelling or attracting each other in the same manner as the Coulomb force between electric charges. The H-field, therefore, is analogous to the electric field E, which starts at a positive electric charge and ends at a negative electric charge. A north pole, then, feels a force in the direction of the H-field while the force on the south pole is opposite to the H-field.
 
Since it is based on the fictitious idea of a magnetic charge density, the Gilbert model has limitations. Magnetic poles cannot exist apart from each other as electric charges can, but always come in north/south pairs. After Ørsted discovered that electric currents produce a magnetic field and Ampere discovered that electric currents attracted and repelled each other similar to magnets, it was natural to hypothesize that all magnetic fields are due to electric current loops.In this model developed by Ampere, the elementary magnetic dipole that makes up all magnets is a sufficiently small Amperian loop of current I. The dipole moment of this loop is m = IA where A is the area of the loop. The force on each magnet depends on its magnetic moment and the magnetic field nb 12 of the other. To understand the force between magnets, it is useful to examine the magnetic pole model given above.One important property of the B-field produced this way is that magnetic B-field lines neither start nor end (mathematically, B is a solenoidal vector field ); a field line either extends to infinity or wraps around to form a closed curve. The force between two small magnets is quite complicated and depends on the strength and orientation of both magnets and the distance and direction of the magnets relative to each other. The force is particularly sensitive to rotations of the magnets due to magnetic torque.If this H-field is the same at both poles of the second magnet then there is no net force on that magnet since the force is opposite for opposite poles. If, however, the magnetic field of the first magnet is nonuniform (such as the H near one of its poles), each pole of the second magnet sees a different field and is subject to a different force. This difference in the two forces moves the magnet in the direction of increasing magnetic field and may also cause a net torque.This is a specific example of a general rule that magnets are attracted (or repulsed depending on the orientation of the magnet) into regions of higher magnetic field. Any non-uniform magnetic field, whether caused by permanent magnets or electric currents, exerts a force on a small magnet in this way. In this example, the magnetic field of the stationary magnet creates a magnetic torque on the magnet that is free to rotate. This magnetic torque τ tends to align a magnet`s poles with the magnetic field lines.