Magnetic permeability is the ability of a material to become magnetized in a magnetic field. It is measured in henres per meter or newton per ampere squared. Air in a vacuum has a constant value called the magnetic constant. Permeability changes with location, frequency, humidity, temperature, and other factors. Substances are classified as paramagnetic, diamagnetic, or ferromagnetic, with ferromagnetic metals having the highest permeability. Ferromagnetic materials can become hard or soft magnets, with hard magnets retaining their magnetism even when the magnetic field is removed.
Some materials become magnetized when placed in a magnetic field; the ability of a material to become magnetized is called its magnetic permeability. An example is the rubbing of a piece of iron with a magnet: the iron will become magnetised and have its own magnetic field, which means that it will have a certain degree of magnetic permeability.
Many substances, even water, have a degree of magnetic permeability. When a material is placed in a magnetic field, it interacts with the field in one way or another. The permeability of a substance describes how the material responds and the effects of the field on the material. A substance with magnetic permeability will become magnetized in the direction of or against the field. Therefore, depending on the permeability, the substance will be attracted or repelled by the field.
Permeability measurement
Scientists represent magnetic permeability with the Greek letter, mu (μ). The International System of Units (SI) measures permeability in henres per meter (H/m) or newton per ampere squared (N/A2). Air in a vacuum, also called free space, has a constant value which is called the magnetic constant. This value is represented by the symbol μ0 and is evaluated as 4π×10−7 H/m which is approximately 1.2566×10−6 H/m. The numerical value is the same when measured in N/A2.
Magnetic permeability, on the other hand, is not a constant figure; rather, it changes with the material’s location in relation to the magnetic field, field frequency, humidity, temperature, and other factors. Knowing the permeability of a material can also be useful for various industries, for example materials with high permeability are used in a variety of applications including electromagnets, transformers and inductors.
Permeability of substances
Substances can also be characterized based on their magnetic permeability, and the permeability level of a substance is indicated as a pure number. If a substance is classified as paramagnetic, its permeability is measured as slightly more than one and such substances are weakly attracted to magnets. If a substance is classified as diamagnetic, the permeability is measured as less than one and that substance will be repelled by a magnet.
Permeability of ferromagnetic metals
A material can also be classified as ferromagnetic; ferromagnetic metals have the highest permeability of all substances and will magnetize when exposed to a magnetic field. As the magnetic field to which the ferromagnetic substance is exposed increases, the magnetic permeability will increase until it reaches its maximum value, at which point it will decrease. Some ferromagnetic materials will become hard or soft magnets; in materials that become soft magnets, such as those materials used in electromagnets, the material will lose its magnetism as the magnetic field is removed. However, hard magnets are difficult to magnetize, but will remain magnetized even when the magnetic field is removed.
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