Table magnetic

Concept: Surface magnetism refers to the magnetic induction intensity at a certain point on the surface of the magnet (then the surface magnetism at the center and the edge is different), which is the value measured by the Gauss meter in contact with a certain surface of the magnet, not the overall magnetic performance of the magnet.


Measurement: Gauss meter, also called Tesla meter, is generally used to measure the magnetism of the magnet. The Hall sensing elements on the gauss meter of different manufacturers are different, and the surface magnetism measured by the same magnet is also different. In addition, it should be noted that the g gauss meter measurement standards used in different countries are different.


The surface magnetism is related to the height-to-diameter ratio of the magnet (the ratio of the height to the diameter of the magnet). The larger the height-to-diameter ratio, the higher the surface magnetism, that is, the larger the surface area perpendicular to the magnetization direction, the lower the surface magnetism; the larger the magnetization direction, The higher the surface magnetism.


Magnetic flux

Concept: Assuming that in a uniform magnetic field with magnetic induction intensity B, there is a plane with area S and perpendicular to the direction of the magnetic field, the product of magnetic induction intensity B and area S is called the magnetic flux passing through this plane, referred to as magnetic flux, symbol " Φ", the unit is Weber (Wb). Magnetic flux is a physical quantity that represents the distribution of the magnetic field. It is a scalar quantity, but it has a positive or negative sign, which only represents its direction. Φ=B·S, when there is an angle θ between the vertical plane of S and B, Φ=B·S·cosθ .


The magnitude of the magnetic flux passing through a plane can be visualized by the number of magnetic lines passing through the plane. In the same magnetic field, where the magnetic induction intensity is greater, the magnetic induction lines are denser. Therefore, the larger B is, the larger S is, the larger the magnetic flux is, which means that the number of magnetic induction lines passing through this surface is more. If there are two magnetic fluxes in opposite directions passing through a plane, the resulting magnetic flux at this time is the algebraic sum of the magnetic fluxes in opposite directions.


Measurement: The fluxmeter is an instrument for measuring magnetic flux, and it needs to cooperate with the measuring coil (copper wire with a diameter of 0.1-0.5). In recent years, domestic permanent magnet manufacturers have widely used Helmholtz coils to detect batch products (Helmholtz coils) The Helmholtz coil is a device that produces a uniform magnetic field in a small area. Due to the open nature of the Helmholtz coil, other instruments can be easily placed in or removed, and visual observation can also be done directly, so it is often used in physical experiments. device. Named after the German physicist Hermann von Helmholtz)



Concept: Remanence refers to the magnetic induction intensity retained in the ferromagnet when the external magnetic field is used to magnetize the ferromagnet to a saturated state and then gradually reduces the external magnetic field to zero. The full name is the residual magnetic induction intensity (indicated by Br). The remanence is determined by the characteristics of the magnet itself. The remanence of the same magnet is constant under certain conditions and has a single value.


The relationship between remanence and surface magnetism: Both are in Gauss, but there is no corresponding relationship between surface magnetism and remanence, that is, two magnets with the same remanence may not have the same size of surface magnetism, and the surface magnetism is magnetized. The influence of shape, size and magnetization mode.


1) For two magnets with the same shape, performance and size, the one with higher surface magnetism has stronger residual magnetism.

2) For two magnets with different shapes, or different performances and sizes, the magnitude of the residual magnetism cannot be simply judged by the height of the surface magnetism.


The relationship between residual magnetism and magnetic flux: When the magnetic circuit of a magnet is closed, a fluxmeter can be used to measure the magnetic flux, and then the residual magnetism can be calculated. Br=φ/n/s, where: φ represents the magnetic flux, n represents the number of coils turned, s represents the cross-sectional area of the magnet.



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