## Magnetic Field Characteristics

**Magnetic Field Characteristics**

The range of dates permitted with the International Geomagnetic Reference Field (IGRF-12) ranges from 1900 and 2020. As is the case for the force between magnets, the magnetic pole model leads more readily to the correct equation. Here, two equal and opposite magnetic charges experiencing the same H also experience equal and opposite forces. Since these equal and opposite forces are in different locations, this produces a torque proportional to the distance (perpendicular to the force) between them. Here, it is the B field interacting with the Amperian current loop through a Lorentz force described below.The big-hearted, big-chorused” (The Guardian) band began in 2007 as a whimsical collaboration among friends. Currents of electric charges both generate a magnetic field and feel a force due to magnetic B-fields. Right hand grip rule : a current flowing in the direction of the white arrow produces a magnetic field shown by the red arrows. Charged particle drifts in a magnetic field with (A) no net force, (B) an electric field, E, (C) a charge independent force, F (e.g. gravity), and (D) an inhomogeneous magnetic field, grad H. It can only do work indirectly, via the electric field generated by a changing magnetic field.Optical Illusions can use color, light and patterns to create images that can be deceptive or misleading to our brains. Where the integral sums over the wire length where vector dℓ is the vector line element with direction in the same sense as the current I, μ0 is the magnetic constant , r is the distance between the location of dℓ and the location where the magnetic field is calculated, and r̂ is a unit vector in the direction of r. Because the magnetic force is always perpendicular to the motion, the magnetic field can do no work on an isolated charge.At first glance, it may appear to be a simple brick wall- but take a closer look and you might just see something else. Where F is the force , q is the electric charge of the particle, v is the instantaneous velocity of the particle, and B is the magnetic field (in teslas ). The Lorentz force is always perpendicular to both the velocity of the particle and the magnetic field that created it. When a charged particle moves in a static magnetic field, it traces a helical path in which the helix axis is parallel to the magnetic field, and in which the speed of the particle remains constant.Perhaps the rapidity of the changes from one of these paces to the other created an optical illusion, which might thus magnify the powers of the beast; for it is certain that Heyward, who possessed a true eye for the merits of a horse, was unable, with his utmost ingenuity, to decide by what sort of movement his pursuer worked his sinuous way on his footsteps with such persevering hardihood. It is often claimed that the magnetic force can do work to a non-elementary magnetic dipole , or to charged particles whose motion is constrained by other forces, but this is incorrect 23 because the work in those cases is performed by the electric forces of the charges deflected by the magnetic field. If both the speed and the charge are reversed then the direction of the force remains the same.

The right-hand rule : Pointing the thumb of the right hand in the direction of the conventional current and the fingers in the direction of B the force on the current points out of the palm. The direction of force on a charge or a current can be determined by a mnemonic known as the right-hand rule (see the figure). Using the right hand and pointing the thumb in the direction of the moving positive charge or positive current and the fingers in the direction of the magnetic field the resulting force on the charge points outwards from the palm.For that reason a magnetic field measurement (by itself) cannot distinguish whether there is a positive charge moving to the right or a negative charge moving to the left. The formulas derived for the magnetic field above are correct when dealing with the entire current. A magnetic material placed inside a magnetic field, though, generates its own bound current , which can be a challenge to calculate. It is defined as the net magnetic dipole moment per unit volume of that region.The magnetization of a uniform magnet is therefore a material constant, equal to the magnetic moment m of the magnet divided by its volume. Since the SI unit of magnetic moment is A.m2, the SI unit of magnetization M is ampere per meter, identical to that of the H-field. The H field lines loop only around `free current` and, unlike the magnetic B field, begins and ends near magnetic poles as well.Where the integral is a closed surface integral over the closed surface S and qM is the `magnetic charge` (in units of magnetic flux ) enclosed by S. (A closed surface completely surrounds a region with no holes to let any field lines escape.) The negative sign occurs because the magnetization field moves from south to north. Where H0 is the applied magnetic field due only to the free currents and Hd is the demagnetizing field due only to the bound currents. The magnetic H-field, therefore, re-factors the bound current in terms of `magnetic charges`. Paramagnetic materials 27 produce a magnetization in the same direction as the applied magnetic field.Superconductors (and ferromagnetic superconductors ) 30 31 are materials that are characterized by perfect conductivity below a critical temperature and magnetic field. They also are highly magnetic and can be perfect diamagnets below a lower critical magnetic field. Superconductors often have a broad range of temperatures and magnetic fields (the so-named mixed state ) under which they exhibit a complex hysteretic dependence of M on B.

Energy is needed to generate a magnetic field both to work against the electric field that a changing magnetic field creates and to change the magnetization of any material within the magnetic field. For non-dispersive materials this same energy is released when the magnetic field is destroyed so that this energy can be modeled as being stored in the magnetic field.If there are no magnetic materials around then μ can be replaced by μ0. The above equation cannot be used for nonlinear materials, though; a more general expression given below must be used. Once the relationship between H and B is known this equation is used to determine the work needed to reach a given magnetic state. For hysteretic materials such as ferromagnets and superconductors, the work needed also depends on how the magnetic field is created.Similar to the way that a changing magnetic field generates an electric field, a changing electric field generates a magnetic field. Thus, a changing electric field generates a changing magnetic field, which generates a changing electric field again. Like all vector fields, a magnetic field has two important mathematical properties that relates it to its sources. Maxwell`s Equations together with the Lorentz force law form a complete description of classical electrodynamics including both electricity and magnetism. A sketch of Earth`s magnetic field representing the source of the field as a magnet.Magnetic field, like all pseudovectors , changes sign when reflected in a mirror: When a current carrying loop (black) is reflected in a mirror (dotted line), its magnetic field (blue) is reflected and reversed. The south pole of that magnet is deep in Earth`s interior below Earth`s North Magnetic Pole. For most locations, the magnetic field has a significant up/down component in addition to the north/south component. Earth`s magnetic field is not constant—the strength of the field and the location of its poles vary.The rotating magnetic field is a key principle in the operation of alternating-current motors A permanent magnet in such a field rotates so as to maintain its alignment with the external field. A rotating magnetic field can be constructed using two orthogonal coils with 90 degrees phase difference in their AC currents. Three similar coils having mutual geometrical angles of 120 degrees create the rotating magnetic field in this case. The resultant voltage in that direction is proportional to the applied magnetic field. Is the magnetomotive force applied to the circuit, and Rm is the reluctance of the circuit.