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Magnetic field similar to a bar magnet

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I I Magnetic field similar to a bar magnet For a very long solenoid, the magnetic field can be considered to be confined to the region inside the coils. – PowerPoint PPT presentation

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Title: Magnetic field similar to a bar magnet


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Magnetic field similar to a bar magnet For a
very long solenoid, the magnetic field can be
considered to be confined to the region inside
the coils.
4
2a
x
z
2a
5
z
x components cancel
?
r
r
z
z gtgt a
?
x
a
a
6
magnetic dipole moment
right hand screw rule
At a point along the axis z gtgt a
i
current loop in xy-plane
7
Diamagnetic material ?m lt 0 (small) B
?o (1 ?m ) H
Permeability ? ?o (1 ?m ) slope of B-H line
8
B
Ideal magnetic material or paramagnetic
material ?m gt 0 (small) B ?o ?r H ? H ?
constant slope of B-H curve
H
9
L11.5 Magnetization
If H is large or substance strongly magnetic
(e.g. ferromagnetic), as H increases, the
magnetization M (and hence B) may increase
nonlinearly
from the graph
Measure
So mr varies with H. Could also use
differential permeability High field region
where slope decreases is called "saturation"
region.
10
L11.6 Magnetization
Hysteresis Ferromagnetic materials also show a
hysteresis effect, where decreasing the applied
magnetic field, or H, doesnt produce the reverse
effect of increasing the field
Br remanence or residual magnetism
Hc coercivity
11
L11.7 Magnetization
hard magnetic materials Hc is high, area of
the loop is large, used for permanent
magnets. soft magnetic materials Hc is small,
area of loop is small, used for transformer cores
electromagnets. Material can be
demagnetized by striking or heating it, or go
round the hysteresis loop, gradually reducing its
size. "Degaussing"
12
L9.1 Magnetic fields due to currents
Magnetic fields are produced by currents.
Biot-Savart law
Example
Amperes law
so
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L9.2 Magnetic fields due to currents
A solenoid
(n is number of turns/length)
Therefore
(inside)
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L9.3 Magnetic fields due to currents
Use the Biot-Savart law to derive the magnetic
field on the axis of a current loop
and
Therefore
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L9.4 Magnetic fields due to currents
Magnetic field of the Earth
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L9.5 Magnetic fields due to currents
The magnetic field of a magnetic dipole
(I??, A?0)
This magnetic field has the same shape as the
electric field of an electric dipole do the
exercise in the Exercise Set.
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Y
X

Z
w
I
t
- - - - - - - - -
charge carriers are electrons for copper Right
hand rule ? electrons are deflected down ? bottom
of probe is negative
B
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Y
X
Z
w
I
t
B
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Saturation of M
retentivity (remanence)
M ? H
coercivity
retentivity (remanence)
Saturation of M
Area enclosed energy dissipated in a cycle in
reversing the magnetic domains
21
H
G
L
K
I
F
E
C
D
I
J
B
A
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