This preview shows pages 1–8. Sign up to view the full content.
1
EEE 224 ELECTROMAGNETIC THEORY
Steady Currents
METU  NCC
Assist. Prof. Dr.
Özlem Özgün
Office
:
S144
Phone
:
661 2972
Email
:
[email protected]
Web
:
http://www.metu.edu.tr/~ozozgun/
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document 2
STEADY ELECTRIC CURRENTS
•
Electrostatics is the study of charges at rest.
•
Now, we shall allow the charges to move, but with a
constant velocity (no time variation).
•
steady electric current = direct current (DC)
0
=
∂
∂
t
3
Types of Current
Convection current
(due to motion of electrons
and/or ions in vacuum or gas)
Conduction current
(due to the drift of valence
electrons in a conductive
medium, such as metal wire)
Separation of charge
Æ
creates electric force (
voltage, potential difference
)
Motion of charge
Æ
creates electric flow (
current
)
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document 4
Current


One ampere
is a number of electrons having a
total charge of 1 C and moving through a given
cross section in 1 s.
Surface S
dq
I
dt
==
=
=
Charge(C)
coulombs
(A)
time(s)
second
5
J
(Amp/m
2
)
Current Density Vector
S
ds
J
J
t
J
n
J
n
t
nt
: normal(perpendicular) component
: tangentialcomponent
J
J
JJ
J
=+
ˆ
ˆ
: normal unit vector
n
n
ds
a ds
a
=
ˆ
n
a
Since
J
t
is due to charges moving tangent to the surface
element (they don’t cross the surface
ds
),
J
t
doesn’t
contribute to the total current crossing the surface.
Current through
ds
:
ˆ
..
nn
d
I
J
d
sJ
a
d
d
s
==
=
Current through
S
:
.
S
IJ
d
s
=
∫
flux of
J
Current & Current Density Vector
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document 6
Current & Current Density Vector
If
S
is a closed surface:
.
S
IJ
d
s
=
∫
v
Total current leaving
(or entering) S
Taken in outward
(or inward) direction
00
vS
dv
ds
∇⋅
∇
⋅=
⇒
⋅
=
∫∫
J=0
JJ
v
If J is solenoidal (or divergenceless)
Divergence
theorem
7
Types of Current (convection current)
Convection current
(due to motion of electrons
and/or ions in vacuum or gas)
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview. Sign up
to
access the rest of the document.
This note was uploaded on 01/07/2011 for the course EE 209 taught by Professor Alexander during the Spring '10 term at Middle East Technical University.
 Spring '10
 alexander
 Electromagnet

Click to edit the document details