ENTC 3331 RF Fundamentals. Dr. Hugh Blanton ENTC 3331. Magnetostatics . Magnetism Chinese—100 BC Arabs—1200 AD Magnetite—Fe 3 O 4 Found near Magnesia (now Turkey) Permanent magnet Not fundamental to magnetostatics. A permanent magnet is equivalent to a polar material in electrostatics.
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Chinese—100 BC
Arabs—1200 AD
Magnetite—Fe3O4
Found near Magnesia (now Turkey)
Permanent magnet
Not fundamental to magnetostatics.
A permanent magnet is equivalent to a polar material in electrostatics.
Equivalent to electrostatics
The theoretical structure of magnetostatics is very similar to electrostatics.
But there is one important empirical fact that accounts for all the differences between the theory of magnetostatics and electrostatics.
There is no magnetic monopole!
MagnetostaticsDr. Blanton  ENTC 3331  Magnetostatics 3
+
N
+
S
N
S
S
+
N
A magnetic monopole does not exist—A magnetostatic field has no sources or sinks!
+
Dr. Blanton  ENTC 3331  Magnetostatics 4
D s
u
rv
D l
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volume
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projection of onto the surface normal
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Conducting MediaDr. Blanton  ENTC 3331  Magnetostatics 11
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constant of proportionality (mobility)
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cylindrical shape.
A2
A1
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Do not confuse charge distribution!
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point of interest
differential section of conductor
contributes to field at
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magnetic field strength
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X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
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X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
righthanded rule
Dr. Blanton  ENTC 3331  Magnetostatics 30
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
righthanded rule
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closed loop = 0
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z
x
at P(x,z), points into the plane
Note that for a small dq, R is approximately unchanged when separated by dq which implies:
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z
y
field by I1 at location of I2
x
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y
x
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Charge is the source of the electrostatic field
No equivalent in magnetostatics
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line differential
field vector of the magnetostatic field
surface
current flowing through the surface
contour
Dr. Blanton  ENTC 3331  Magnetostatics 45
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zaxis
z
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z
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y
0.25m
0.25m
x
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0.25m
0.25m
x
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