This preview shows pages 1–2. Sign up to view the full content.
1
16
Current Density J
area
current
A
i
J
=
=
v
v
J is caused by E, the electric field.
In fact,
E
E
J
v
v
v
σ
ρ
=
=
1
Conductivity is the inverse of Resistivity.
17
One can then show that:
iR
V
=
Δ
J
E
=
They are equivalent.
Macroscopic and Microscopic versions of Ohm’s Law.
18
A copper cylinder is machined to have the following shape.
The
ends are connected to a battery so that a current flows through
the copper.
A
C
B
Which region A, B, or C has the greatest magnitude current i?
A
B
C
D) all three have the same i
Clicker Question
19
A copper cylinder is machined to have the following shape.
The
ends are connected to a battery so that a current flows through
the copper.
A
C
B
Which region A, B, or C has the greatest magnitude current
density J?
A
B
C
D) all three have the same J.
Clicker Question
Region B has the largest current density J = i/A.
All 3 regions have the
same current i, so the region with the smallest A has the largest J.
20
Clicker Question
A copper cylinder is machined to have the following shape.
The
ends are connected to a battery so that a current flows through
the copper.
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.
 Fall '06
 DUBSON
 Conductivity, Current

Click to edit the document details