磁性材料的特性PPT课件

B r B. 0
(16.1)
2
Leabharlann Baidu
B r B0 (16.1)
►
.
3
16.2 Magnetization
► In 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.
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
ferromagnetic material as
shown in Fig.16.4 .
.
9
If the ferromagnetic materials is made to have a hollow interior, such as an iron box , the magnetic field lines would be collected in the iron wall as shown in Fig. 16.5
(16.3) (16.4)
H C
d r . I0,in
(16.5) 7
C H d r 2 rH I
H I
2 r
H r0I
2 r
.
8
16.4 Magnetic Shielding
► When a bock of ferromagnetic
material is put in a magnetic
CHAPTER 16 MAGNETIC PROPERTIES OF MATERIALS
►16.1 Effect on Magnetic Field by Materials ►16.2 Magnetization ►16.3 Vector H and Its Circuital Theorem ►16.4 Magnetic Shielding
In the hollow space in the box ,the magnetic field would be very weak . Thus when something is put in the closed box . It will not (or only slightly) be affected by external magnetic fields . This is the principle of magnetic shielding using iron box.
.
4
Example 16.1 A long straight solenoid of n turn per unit length is filled inside with uniform material of relative permeability . Find the surface bound current density on the surface of the material in the solenoid.
►
B B0 +B ' 0 nI j '
B r 0nI
j
'
r
1
nI .
(16.2) 5
j ' r 1nI
►
.
6
16.3 Vector H and Its Circuital Theorem
B d r 1
C r 0
0
C B0
dr
0 I0,in 0
I0,in
H B / r0 B /
field . Since its is very large.
The surface bound current
produced by magnetization is
very large . The superposition of
the magnetic field produced by
these bound currents on the
.
10
.
1
16.1 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.
original external field would
charge the distribution of the
later drastically. Pictorially , the
resultant field lines would be
concentrated or collected in the