第16章磁性材料的特性.pptxVIP

CHAPTER 16 MAGNETIC PROPERTIES OF MATERIALS16.1 Effect on Magnetic Field by Materials 16.2 Magnetization16.3 Vector H and Its Circuital Theorem 16.4 Magnetic Shielding16.1 Effect on Magnetic Field by Materials The interaction between magnetic fields and materials can be observed experimentally. The most simple method is to use a long straight with vacuum or air inside first (Fig.16.1(a)) and measure the magnetic field in it when current I is flowing in the coils.Next fill the solenoid with some material and then measure again the magnetic field in it when the same current is led in the coils (Fig.16.1(a)) . Let B0 and B be the magnetic field measured in the two cases respectively. Experimental results show that the two differ from each other and can related as ? is called the relative permeability of the matter different for different material. Some materials have constant of values slightly smaller than unit. Such material is called diamagnetic material. Some materials have constant of value slightly larger than unit. Such material is called paramagnetic material. The effects of these two kinds of materials on the magnetic field are very small and then always neglected in ordinary technique. The of the third kind of magnetic material is always much larger than one and also usually changes with the magnitude of B0. Such magnetic media is called ferromagnetic material which interact with magnetic field strongly and hence are always used in electrical and electronic engineering.16.2 MagnetizationIn an atom ,the electrons orbit around the nucleus and have also spin. The nucleus also has spin. These motion all from equivalent circular electric currents . As a whole these motions of charges in a molecule may be considered as constitute a single microscopic circular current called molecular current i with molecular magnetic moment m.Example 16.1 A long straight solenoid of n turn per unit length is filled inside with uniform material of relative permeability . Find the