Physics 121: Electricity & Magnetism – Lecture 12 Carsten Denker NJIT Physics Department Center for Solar–Terrestrial Research
Physics 121: Electricity & Magnetism – Lecture 12 Carsten Denker NJIT Physics Department Center for Solar–Terrestrial Research.
Dec 21, 2015
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Physics 121: Electricity & Magnetism – Lecture 12
Carsten Denker
NJIT Physics DepartmentCenter for Solar–Terrestrial
Research
April 11, 2007 Center for Solar-Terrestrial Research
Gauss’ Law for Magnetic Fields
Gauss’ law
The simplest magnetic structure that can exist is a dipole. Magnetic mono-poles do not exist (as far as we know).
0B B dA
April 11, 2007 Center for Solar-Terrestrial Research
Magnetism and Electrons
Spin magnetic dipole moment
Bohr magneton
Orbital magnetic dipole moment
s
eS
m
249.27 10 J/T4B
eh
m
ext , exts s zU B B
orb orb2
eL
m
orb ext orb, extzU B B
April 11, 2007 Center for Solar-Terrestrial Research
Paramagnetism: A paramagnetic material placed in an external magnetic field develops a magnetic dipole moment in the direction of . If the field is non-uniform, the paramagnetic material is attracted toward a region of greater magnetic field from a region of lesser field.
Magnetic MaterialsDiamagnetism: A diamagnetic material placed in an external magnetic field develops a magnetic dipole moment directed opposite . If the field is non-uniform, the diamagnetic material is repelled from a region of greater magnetic field toward a region of lesser field.
extB
extB
extB
extB
April 11, 2007 Center for Solar-Terrestrial Research
Ferromagnetism
A ferromagnetic material placed in an external magnetic field develops a strong magnetic dipole moment in the direction of . If the field is non-uniform, the ferromagnetic material is attracted toward a region of greater magnetic field from a region of lesser field.
Magnetization curve and hysteresis loop
extB
extB
April 11, 2007 Center for Solar-Terrestrial Research
Induced Magnetic Fields
Maxwell’s law of induction
Ampere-Maxwell law
0 0Ed
B dsdt
0 0 0 encEd
B ds idt
April 11, 2007 Center for Solar-Terrestrial Research
Displacement Current
Displacement current
Ampere-Maxwell law
Inside a circular capacitor
Outside a circular capacitor
022diB rR
,enc 0E
d
di
dt
0 ,enc 0 encdB ds i i
0
2diBr
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