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/his'teuh ree"sis/, n. Physics.1. the lag in response exhibited by a body in reacting to changes in the forces, esp. magnetic forces, affecting it. Cf. magnetic hysteresis.2. the phenomenon exhibited by a system, often a ferromagnetic or imperfectly elastic material, in which the reaction of the system to changes is dependent upon its past reactions to change.[1795-1805; < Gk hystéresis deficiency, state of being behind or late, hence inferior, equiv. to hystere-, var. s. of hystereîn to come late, lag behind, v. deriv. of hýsteros coming behind + -sis -SIS]
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Lagging of the magnetization of ferromagnetic material (see ferromagnetism), such as iron, behind variations of the magnetizing field.When such a material is placed in a coil of wire carrying an electric current, the magnetic field so created forces atoms in the material to align with the field. This increases the total magnetic field to a maximum when all the atoms are aligned, though the total field lags behind the magnetizing field. When the intensity of the magnetizing field is decreased to zero, some field remains in the material, and if the magnetizing field is reversed the total magnetization also reverses but again lags behind. The complete cycle, known as a hysteresis loop, dissipates energy in the form of heat as the magnetization is reversed.* * *
▪ physicslagging of the magnetization of a ferromagnetic material, such as iron, behind variations of the magnetizing field. When ferromagnetic materials are placed within a coil of wire carrying an electric current, the magnetizing field, or magnetic field strength H, caused by the current forces some or all of the atomic magnets in the material to align with the field. The net effect of this alignment is to increase the total magnetic field, or magnetic flux density B. The aligning process does not occur simultaneously or in step with the magnetizing field but lags behind it.If the intensity of the magnetizing field is gradually increased, the magnetic flux density B rises to a maximum, or saturation, value at which all of the atomic magnets are aligned in the same direction. When the magnetizing field is diminished, the magnetic flux density decreases, again lagging behind the change in field strength H. In fact, when H has decreased to zero, B still has a positive value called the remanence, residual induction, or retentivity, which has a high value for permanent magnets. B itself does not become zero until H has reached a negative value. The value of H for which B is zero is called the coercive force. A further increase in H (in the negative direction) causes the flux density to reverse and finally to reach saturation again, when all the atomic magnets are completely aligned in the opposite direction. The cycle may be continued so that the graph of the flux density lagging behind the field strength appears as a complete loop, known as a hysteresis loop. The energy lost as heat, which is known as the hysteresis loss, in reversing the magnetization of the material is proportional to the area of the hysteresis loop. Therefore, cores of transformers are made of materials with narrow hysteresis loops so that little energy will be wasted in the form of heat.* * *
Universalium. 2010.
