II. Electric current
1. Definition
dt
dQ
I
=
Units:
[
I
] = 1A = 1 C/s
Conventional
current
Electron
flow
Example:
10
20
electrons passed through the electric conductor during 4 seconds.
Find the electric current through this conductor.
A
s
C
t
q
I
4
4
)
10
)(
10
6
.
1
(
20
19
=
×
=
=

C
s
A
It
q
5
.
0
)
1
)(
5
.
0
(
=
=
=
C
s
A
It
q
30
)
60
)(
5
.
0
(
=
=
=
Example:
The electric current of 0.5 A is flowing through the electric conductor.
a) What electric charge is passing through the conductor during each second?
b) What electric charge will pass through the conductor during 1 minute?
a)
b)
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
2. Current density
dA
dI
J
=
•
Current density
is a local characteristic defined at a point
•
Current
is not a local characteristic
•
Current density
is a vector directed along the current at a given point
•
Current
is a scalar
•
Both current and current density are macroscopic characteristics
Units:
[
]
(
29
s
m
C
m
A
J
2
2
/
1
/
1
=
=
Current density
J
is a vector quantity whose magnitude
J
is the ratio of
the magnitude of current
dI
flowing in a conductor to the crosssectional
area
dA
perpendicular to the current flow and whose direction points in
the direction of the current.
This is the end of the preview.
Sign up
to
access the rest of the document.
 Fall '09
 MEYER
 DI, current density, internal resistance, current dI

Click to edit the document details