Electromagnetism PHYS20141
Schuster 4-11
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Week 8
- Inductance
- Relative permeability
- Magnetization & magnetic susceptibility
- Mechanisms for magnetization
- diamagnetism
Inductance
- Consider a solenoid
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Magnetic dipoles
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Magnetic susceptibility
� χB < 0 – Diamagnetism - equivalent to induced polarization
� χB > 0 – Paramagnetism- equivalent to intrinsic polarization
NB we will also consider the possibility of a non linear
response M(B) in ferromagnets
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Magnetic susceptibilities
� Glass -1.1 x 10-4
� Gold -3.6 x 10-5
� Copper -9.8 x 10-6
� Water -9.1 x 10-6
� Magnesium 1.2 x 10-3
� Aluminium 2.3 x 10-3
� Tungsten 6.8 x 10-3
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Diamagnetic
Paramagnetic
Electron in orbit = current
Consider an electron orbiting around a nucleus –
motion of electrons = current in opposite direction
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e-
v
L
m
Area, A = πr2 r
Switch on an external field
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e-
v
L
m
Bext
FORCE = -ev x B
FORCE = qE
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As per dielectrics…
- Mechanisms for magnetization- Paramagnetism
- Bound current & surface current
- Magnetostatic equations in magnet
- Interfaces between magnets
Paramagnetism
� Consider a material with intrinsic
magnetic dipoles
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Paramagnetism
� Alignment of intrinsic magnetic dipoles
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Diamagnetism &
paramagnetism
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Increases field
inside the magnet
Decreases field
inside the magnet
Magnetostatics in a magnet
In dielectrics there is a bound charge density ρbound and a surface charge σP.
In a magnet there is a equivalent bound current density
and surface current (see Grant and Phillips for
derivation Pgs 181-187)
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Bound & surface current
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Return to the solenoid
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B⊥ is continuous
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H// is continuous
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