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Magnetic induction B (also known as magnetic flux density) has the SI unit tesla [T or Wb/m 2]. [1] One tesla is equal to 10 4 gauss. Magnetic field drops off as the inverse cube of the distance ( 1 / distance 3 ) from a dipole source. Energy required to produce laboratory magnetic fields increases with the square of magnetic field. [2]
It is the ratio of magnetization M (magnetic moment per unit volume) to the applied magnetic field intensity H. This allows a simple classification, into two categories, of most materials' responses to an applied magnetic field: an alignment with the magnetic field, χ > 0 , called paramagnetism , or an alignment against the field, χ < 0 ...
The gauss is the unit of magnetic flux density B in the system of Gaussian units and is equal to Mx/cm 2 or g/Bi/s 2, while the oersted is the unit of H-field. One tesla (T) corresponds to 10 4 gauss, and one ampere (A) per metre corresponds to 4π × 10 −3 oersted .
A good bar magnet may have a magnetic moment of magnitude 0.1 A·m 2 and a volume of 1 cm 3, or 1×10 −6 m 3, and therefore an average magnetization magnitude is 100,000 A/m. Iron can have a magnetization of around a million amperes per meter.
The energy of a localized magnetic charge q m in a magnetic scalar potential is =, and of a magnetic charge density distribution ρ m in space =, where µ 0 is the vacuum permeability. This is analog to the energy Q = q V E {\displaystyle Q=qV_{E}} of an electric charge q in an electric potential V E {\displaystyle V_{E}} .
For an electromagnet with a cylindrical bore, producing a pure multipole field of order , the stored magnetic energy is: =!. Here, is the permeability of free space, is the effective length of the magnet (the length of the magnet, including the fringing fields), is the number of turns in one of the coils (such that the entire device has turns), and is the current flowing in the coils.
In magnetics, the maximum energy product is an important figure-of-merit for the strength of a permanent magnet material. It is often denoted (BH) max and is typically given in units of either kJ/m 3 (kilojoules per cubic meter, in SI electromagnetism) or MGOe (mega-gauss-oersted, in gaussian electromagnetism). [1] [2] 1 MGOe is equivalent to 7 ...
If the magnetic field is now reduced monotonically, M follows a different curve. At zero field strength, the magnetization is offset from the origin by an amount called the remanence. If the H-M relationship is plotted for all strengths of applied magnetic field the result is a hysteresis loop called the main loop.